Hypoplastic right heart syndrome encompasses a spectrum of cardiac lesions characterized by pulmonary atresia (either a formed but imperforate pulmonary valve, also known as membranous atresia, or long-segment muscular atresia), varying degrees of RV hypoplasia, and an intact ventricular septum. This class of cardiac defects is often referred to as pulmonary atresia/intact ventricular septum. The tricuspid valve is patent but hypoplastic, with the degree of tricuspid hypoplasia generally correlating with the extent of RV hypoplasia. In moderate hypoplasia, only two major portions of the RV (inflow and outflow) are present; the apical (trabecular) portion is either truncated or absent. This is termed a “bipartite” RV. In the most severe cases, only a tiny RV (usually the inflow portion) is present and this is termed a “unipartite” RV. Such patients have an obligate right to left shunt across the atrial septum, and a good-sized LV and aortic valve. Given the absence of antegrade flow from RV to pulmonary artery, patients require an alternate source of pulmonary blood flow, usually from a patent ductus arteriosus (PDA). As RV hypoplasia becomes more severe, there is an increasing likelihood of persistent embryonic sinusoidal connections (also known as ventriculo-coronary arterial communications) between the RV and the epicardial coronary arteries [8]. Some of these sinusoidal connections can contain stenoses that result in portions of the myocardium being perfused primarily or exclusively by the hypertensive RV; this situation is termed RV dependent coronary artery perfusion. In such cases, a two ventricle repair cannot even be considered, as the RV cannot be decompressed [9].

In the absence of RV-dependent coronary circulation, a determination must be made whether a hypoplastic right heart syndrome patient is a candidate for a two ventricle repair, or whether the patient should undergo single ventricle palliation. This determination is largely based upon an assessment of the degree of RV hypoplasia, which in turn is based primarily upon an evaluation of tricuspid valve annulus and RV size. The minimum tricuspid and RV dimensions that dictate the choice of one vs. two ventricle strategy vary among different institutions, and the published criteria continue to be evolve with time and increasing experience. Some centers use a tricuspid valve annulus z score anywhere between <−3 to −10 as a cutoff [10–13], some use the RV morphology (unipartite vs. bi/tripartite) [14], some use an estimation of RV diastolic volume [15], and some use a combination of these criteria. Whatever the method, if the tricuspid valve and RV are deemed too hypoplastic for a two ventricle circulation, then initial surgery is undertaken with the intention of single ventricle palliation—specifically, planned future bidirectional Glenn and Fontan procedures (discussed below). In this case, a systemic-pulmonary artery shunt (Blalock-Taussig shunt) is initially performed, often in conjunction with an atrial septectomy to assure unobstructed mixing of right and left atrial blood. In patients with milder forms of tricuspid valve and RV hypoplasia, a two ventricle (vs. “one and a half”) approach can be considered. In these instances antegrade flow across the RV outflow tract is established in the newborn period, with the expectation that the increased blood flow through the RV will stimulate growth of this chamber. This can be accomplished surgically by reconstruction of the RV outflow tract, usually performed in combination with a systemic-pulmonary shunt (such as a Blalock-Taussig shunt) [16]. An alternative strategy utilizes interventional catheterization techniques to establish antegrade flow across the RV outflow tract, including catheter perforation of the pulmonary valve (using balloon, laser, or radiofrequency methods), along with transcatheter stenting of the ductus arteriosus [14, 17]. With either surgical or transcatheter approach, some patients experience enough growth of their RV that they can function effectively with two ventricle physiology [14, 18]. Eventually, these patients can undergo closure of the systemic-pulmonary shunt and, if an atrial defect is still present, it can also be closed. In other patients, the RV continues to be moderately hypoplastic and a “one and a half repair” is subsequently undertaken. In this type of operation, a bidirectional Glenn procedure (discussed below) is performed to allow SVC blood to drain directly to the pulmonary arteries, while leaving inferior vena cava (IVC) blood to return to the RV and then be ejected directly into the main and branch pulmonary arteries. At the time of the Glenn operation, the atrial septal defect, if present, is often closed [19].

The TEE evaluation of the patient with hypoplastic right heart syndrome focuses on the adequacy of an interatrial communication, as well as the degree of tricuspid valve and RV hypoplasia. The atrial septum can be assessed from the ME 4 Ch and mid esophageal bicaval (ME Bicaval) views. The tricuspid valve and hypoplastic RV are best seen using a combination of MV 4 Ch (Fig. 10.2a, Video 10.2) and mid esophageal right ventricle inflow-outflow (ME RV In-Out) views (Fig. 10.2b, c, Video 10.2). Tricuspid and pulmonary valve annular diameters can also be measured using these views; as mentioned above, the tricuspid valve annulus diameter plays a very important role in determining whether intervention should be undertaken for a one or two ventricle strategy [15, 19, 20]. Coronary artery sinusoidal flow can sometimes be seen with color flow Doppler, but coronary artery stenoses cannot be diagnosed by echocardiography and therefore must be evaluated by angiography. Left ventricular and mitral valve function should be evaluated carefully, also from the midesophageal views, specifically the ME 4 Ch, mid esophageal two chamber (ME 2 Ch), mitral commissural (ME Mitral), and long axis (ME LAX) views. Additional information regarding LV and mitral valve function can be provided by the transgastric views: the transgastric basal and mid short axis (TG Basal SAX, TG Mid SAX) and transgastric two-chamber (TG 2 Ch) and transgastric long axis (TG LAX) views. Some patients can have significant LV outflow tract obstruction due to bowing of the ventricular septum that produces mid-cavitary obstruction, and this should also be evaluated carefully with a combination of mid esophageal (ME 4 Ch, ME LAX), transgastric (TG LAX), and deep transgastric long axis (DTG LAX) and deep transgastric sagittal (DTG Sagittal) views. The pulmonary valve, if present, can be evaluated and its annulus measured in the ME RV In-Out view, using a multiplane angle of 60–90° (Fig. 10.2b). The branch pulmonary arteries and ductus arteriosus are not always well seen, but ductal left to right flow can often be detected by color flow Doppler in the UE PA LAX and UE Ao Arch SAX views, using leftward probe rotation (when there is a left aortic arch).

Patients with tricuspid atresia have no functional tricuspid valve. Often, there is complete absence of the tricuspid valve, with only a muscular shelf seen in the tricuspid position. In some instances the tricuspid valve is formed and present but imperforate (so-called “membranous” tricuspid atresia). In either case, there is obligate right to left shunting across the atrial septum, and complete mixing of deoxygenated and oxygenated blood at atrial level. There is generally a small RV cavity, with marked hypoplasia of the inflow portion but variable trabecular and infundibular portions, and usually (but not always) a communication between the LV and the hypoplastic RV. This communication has variously been termed a ventricular septal defect (VSD), or alternatively a bulboventricular foramen (BVF) [21, 22]—it generally is located between the LV and RV inflow portion, but can also be seen closer to the apex or infundibulum of the small RV. In the majority of cases, this defect will be the site of obstruction to LV to RV shunting, though obstruction can occur at the outlet valve itself (the valve arising from the RV) or in the subvalvar infundibulum [21]. The ventriculo-arterial connection can vary, and one of the most recognized classification systems for tricuspid atresia is based upon the relationship of the great arteries [23]. A summary of this classification system is given in Table 10.1. In general, this system’s nomenclature is not widely used when clinicians describe and discuss tricuspid atresia, but it still serves to underline the most important anatomic features relevant to this anomaly, namely (a) great artery origin/relationship, (b) VSD/BVF size, and (c) whether aortic or pulmonary outflow obstruction is present. In Type I, seen in 70–80 % of patients with tricuspid atresia [24], the aorta arises in normal position from the LV, there is ventriculo-arterial concordance, and the aortic valve is of normal size and function. The pulmonary artery arises from the small RV chamber, and the amount of pulmonary blood flow depends upon the size of the VSD/BVF and the degree of subpulmonary stenosis (if present). Type I can be further classified into three subtypes, based upon the size of the VSD and degree of pulmonary outflow obstruction: Type Ia (no VSD, pulmonary atresia), Type Ib (small VSD, pulmonary stenosis); Type Ic (large VSD, no pulmonary stenosis). If the ventricular defect is large and there is no subpulmonary stenosis, the patient can have excessive pulmonary blood flow leading to pulmonary overcirculation and congestion. If there is obstruction at the ventricular defect or subpulmonary level, there can be reduced antegrade flow leading to systemic arterial hypoxemia (Fig. 10.3, Video 10.3). The patient is then dependent upon an alternative source of pulmonary blood flow such as a patent ductus arteriosus or surgically created shunt. With Type II, seen in 12–25 % of patients with tricuspid atresia [24], there are transposed great arteries (ventriculo-arterial discordance), and the aorta arises from the small RV outflow chamber, generally to the right of the pulmonary artery, or D-transposed. Type II is also classified into three subgroups, based on the degree of pulmonary outflow obstruction: Type IIa (pulmonary atresia), Type IIb (pulmonary stenosis), Type IIc (no pulmonary stenosis). In general, with Type II tricuspid atresia there is either subaortic stenosis or subpulmonary stenosis, depending on the size of the VSD/BVF (through which blood must pass from LV to RV to aorta) and position of the infundibular septum. Type IIc is the most common form: in such cases the pulmonary valve (which arises from the LV) is usually of normal size and function. The ventricular defect is often surrounded by a muscular rim, and if small enough, there can be marked subaortic stenosis, often in association with hypoplasia of the aorta and aortic coarctation or interruption (in many cases requiring a patent ductus arteriosus for systemic perfusion). Such patients invariably require surgery to alleviate or bypass the subaortic stenosis, as well as repair the aortic arch. Conversely, Types IIa and IIb (which are much less common) have pulmonary outflow obstruction, usually due to posterior malalignment of infundibular septum that can produce significant subpulmonary stenosis and decreased pulmonary blood flow [25]. Such patients might require an alternative source of pulmonary blood flow, such as a ductus arteriosus or surgically created shunt. In these instances the VSD/BVF and aorta are generally of good size, and there is no obstruction to systemic blood flow. Types I and II are by far the most common forms of tricuspid atresia. Type III is much more rare, seen in about 3–6 % of patients with tricuspid atresia, and it is a less specific category that includes a number of other defects such as L-transposition of the great arteries, truncus arteriosus, etc. [24].

The TEE evaluation of tricuspid atresia focuses upon atrial septal patency and shunting, mitral valve and LV function, the position of the great arteries and ventriculo-arterial relationship, and outflow tract patency including the size of the VSD/BVF. Much of this evaluation can be performed from the level of the mid esophagus, particularly the ME 4 Ch view for evaluation of atrial septum, mitral valve, LV and great arteries as well as VSD/BVF. Supplemental evaluation of these structures can also be provided by other mid esophageal views: ME Bicaval (systemic venous return, atrial septum), ME LAX (mitral valve, semilunar valves, VSD/BVF), ME RV In-Out (VSD/BVF). The deep transgastric views (DTG LAX, DTG Sagittal) can also provide good visualization of the mitral valve and VSD/BVF, as well as the aortic and pulmonary outflow tracts. The DTG views are also useful for spectral Doppler evaluation of the outflow tracts. In patients with transposed great arteries, the size of the ventricular defect, and potential for subaortic stenosis, should be evaluated carefully (Fig. 10.4, Video 10.4). If the VSD/BVF and/or the subaortic area are felt to be potentially obstructive, the pulmonary valve should be evaluated with the anticipation of a possible Damus-Kaye-Stansel (DKS) operation. The evaluation of the VSD/BVF and the DKS operation are discussed below. In tricuspid atresia patients with transposed great arteries, left juxtaposition of the atrial appendages can sometimes be encountered [26, 27]. Care should be taken to recognize this entity and not confuse it with a large atrial septal defect; in fact, the orientation of the true atrial septal defect is often different from what is normally encountered [28]. This entity is best evaluated from a modified ME AV SAX view first retroflexed, then slowly anteflexed to demonstrate the right atrial appendage just anterior to the left atrial appendage. An example of left juxtaposition of the atrial appendages is given in Chap.​ 12—Conotruncal Malformations.

In tricuspid atresia patients with normally related great arteries, the size of the interventricular communication and determination of the presence and degree of pulmonary outflow tract obstruction are essential. If pulmonary blood flow is unobstructed, limitation by means of pulmonary artery banding is usually undertaken; if blood flow is reduced, interventions to increase pulmonary blood flow will need to be considered. Some patients have just enough restriction to pulmonary blood flow that they are neither overcirculated nor excessively cyanotic—in other words, they are well balanced. Such patients might not require any intervention for the first few months of their life, although ultimately they will require the same surgeries used for all single ventricle patients—namely, the Glenn and Fontan procedures (discussed below).

This category of single ventricle includes those defects in which both atria empty completely (or almost completely) into one large ventricle. A second ventricle might or might not be present; if present, it is generally quite hypoplastic. This group of defects includes unbalanced AV septal defect, double inlet ventricle (DILV), as well as the rare double inlet right ventricle (DIRV) and true single (or solitary) ventricular chamber of indeterminate morphology.

Patients with unbalanced AV septal defects have similar characteristics to a large AV septal defect (Chap.​ 8—AV septal defects and AV valve anomalies), but the common AV valve—instead of being balanced equally over both ventricles—is oriented significantly toward one ventricle. Thus, both atria empty primarily or almost completely into that chamber, and there is usually some degree of hypoplasia of the other ventricle (Fig. 10.5). In some patients, the degree of AV valve unbalance is so pronounced, and/or the degree of ventricular hypoplasia so apparent, that it is clear that the defect cannot be septated — i.e. the patient must be treated as a functional single ventricle. In others, this assessment is more difficult, and various criteria are utilized to determine whether a biventricular repair is feasible [29, 30]. Unbalanced AV septal defect is a common accompanying feature of heterotaxy syndrome (discussed below). The TEE evaluation of such patients is very much the same as for any patient with an AV septal defect, with particular attention paid to the degree of common AV valve distribution or commitment to the underlying ventricular chambers, AV valve function, ventricular hypoplasia, and possible aortic or pulmonary outflow tract obstruction. A combination of mid esophageal views (ME 4 Ch, ME 2 Ch, ME LAX) are best for evaluating the common AV valve and ventricular chambers, and also the degree of AV valve regurgitation (if present). When available, the deep transgastric views (DTG LAX, DTG Sagittal) can be used to evaluate the AV valve en face and its balance over both ventricles, similar to the views obtained with a subcostal sagittal view [29, 31]. The TEE evaluation of AV septal defects is discussed extensively in Chap.​ 8.

Double inlet ventricles are characterized by both atria and AV valves emptying into a large ventricle of either left or right ventricle morphology. The vast majority of these are DILV: both AV valves empty into a large ventricle of LV morphology, and there is generally a smaller RV outflow chamber located anteriorly. In many cases of DILV, it is very difficult to determine which AV valve is tricuspid, and which is mitral. There are three general classes of DILV: (1) normally related great arteries; (2) D-transposed great arteries; (3) L-transposed great arteries. The patient with DILV and normally related great arteries, also known as a Holmes’ heart [32], has a normal aortic valve and aorta arising from the large LV, with the pulmonary artery arising from the RV outflow chamber with a variable degree of subpulmonary stenosis (Fig. 10.6, Video 10.5). The patient with DILV and D-transposed great arteries has the aorta arising from a rightward, RV outflow chamber; with L-transposed great arteries the aorta arises from a leftward RV outflow chamber. Of the three types of DILV, the L-transposed is the most common type (60–65 % of all DILV), followed by the D-transposed form (20–25 %), and lastly the normally related great arteries variation (15 %). In both forms of DILV with transposed great arteries, there is either significant subaortic narrowing (often with ascending aorta and aortic arch hypoplasia) or subpulmonary narrowing, depending on the size of the VSD/BVF and position of the infundibular septum [1, 33]. This is analogous to tricuspid atresia and transposed great arteries, as described above.

DIRV is a rare defect in which both AV valves empty into a chamber of RV morphology [34]. In these instances, there are prominent muscle bundles in the large RV chamber; occasionally a large muscle bar is present that can be confused for a remnant of ventricular septum [35]. Usually, both great arteries also emerge from the same large RV, thus this lesion is often termed a double inlet, double outlet RV [35]. However unlike DILV, no anterior outflow chamber is visible. Instead, a rudimentary LV chamber may or may not be present; when present, it is located posteriorly, with no outflow to either great artery (Fig. 10.7, Video 10.6). Varying degrees of obstruction to one of the great arteries (generally the pulmonary trunk) can also be seen [36].

In the true single ventricle, there is no visible second chamber, and the large solitary ventricle has a very primitive morphology that eludes definitive identification as either an RV or LV [4, 33, 37]. There can be either one or two AV valves emptying into the large chamber, or there can even be one large common AV valve (i.e. a large common AV canal). Often, the heart has a very primitive appearance, with bizarre and loose muscular trabeculations seen in the large ventricular cavity. The great arteries have a variable relationship, generally with either stenosis of the aortic or pulmonary artery outflow tracts. There is a higher prevalence of atrial isomerism with indeterminate ventricular morphology [38].

Evaluation of the univentricular heart by TEE is similar to the evaluation of tricuspid atresia. The views of the inflows are best obtained beginning with the lower esophageal situs short axis (LE Situs SAX), first using a multiplane angle of 0–20°, then withdrawing the probe to visualize the junction between IVC and right atrium. Further withdrawal of the probe to the ME 4 Ch view demonstrates the AV valve(s) by imaging. Both color flow and spectral Doppler are necessary to evaluate AV valve function. When two AV valves are present, if either AV valve is stenotic or atretic, patency of the atrial septum must be assessed both by imaging and color flow Doppler. The relationship of the great arteries must also be determined; if one of these arises from a smaller outflow chamber, the VSD/BVF size and patency also need to be evaluated, preferably from several multiplane angles between 0 and 90°. Any subpulmonary or subaortic stenosis can be well visualized from a ME RV In-Out, ME AV LAX, and ME LAX views, multiplane angles between 70° and 120°, optimized to yield the best longitudinal view of the outflow tract (Fig. 10.8, Video 10.7). When available, the deep transgastric windows (DTG LAX, DTG Sagittal) provide good visualization of a number of structures, including the VSD/BVF, as well as excellent angles of Doppler interrogation for gradients across either the aortic or pulmonary outflow tracts (Fig. 10.9).

As with tricuspid atresia, left juxtaposition of the atrial appendages is also associated with DILV and D-transposed great arteries, and care should be taken not to confuse this entity with a large atrial septal defect.

Despite an external appearance of right-left symmetry, much of the human body’s internal organ layout is in fact asymmetric, and this asymmetry leads to a definition of normal (and abnormal) sidedness. In situs solitus (which typifies most humans), the liver and IVC are on the right, the stomach and aorta on the left. The heart, being an asymmetric organ, also lateralizes to lie in the left chest. In situs inversus, the organs lateralize to the opposite side, producing a “mirror image” layout of the heart, lungs, and abdominal viscera. The term heterotaxy denotes an abnormality of laterality, or sidedness, in which there is (paradoxically) bilateral visceroatrial symmetry. Hence this condition is known as situs ambiguous or atrial isomerism and involves multiple organ systems in the body, including the heart. From a genetic standpoint, it is now known that heterotaxy belongs to a class of abnormalities known as “ciliopathies”, characterized by abnormalities or dysfunction of primary cilia. During cardiac embryogenesis, primary cilia on the embryonic node are required for generation of the left-right axis. Ciliary dysfunction abnormalities are responsible for disorders of left-right axis determination during early embryonic development. This results in a disorder of laterality, manifested by abnormalities of any internal organ that is asymmetrically position—including the heart. Significant phenotypic variation can result [39, 40].

Patients with heterotaxy generally have significant cardiac abnormalities, often affecting multiple segments of the heart [41–43]. However despite the myriad potential variations in cardiac anatomy, heterotaxy patients tend to fall into one of two categories: (1) right isomerism (bilateral right-sidedness), or asplenia; (2) left isomerism (bilateral left-sidedness), or polysplenia. The visceral and cardiac variants most commonly seen with each category are listed in Table 10.2. It is important to note, however, that this table lists only the most commonly associated features seen with each category, and a number of exceptions have been reported, as well as considerable overlap between the two categories.

For most heterotaxy patients, especially those with right isomerism (asplenia), the preponderance of cardiac abnormalities—particularly hypoplasia of one ventricle—dictates that a single ventricle pathway be chosen [44, 45]. However in a small percentage of patients (mainly those with left isomerism, or polysplenia), a two ventricle approach can be contemplated [46, 47]. Therefore when a TEE evaluation of either right or left isomerism is performed, a very careful and comprehensive evaluation is recommended in consideration of the implications regarding patient management. Because of potential for anatomic abnormalities at multiple levels, a complete, segmental examination (Chap.​ 4) should be performed, particularly in those patients with unknown or uncertain anatomy. Using the many available TEE views discussed in Chap.​ 4 as well as this chapter, careful attention should be paid to systemic and pulmonary venous drainage, number and function of the AV valves, ventricular size and function, great artery position, and possible outflow tract stenosis. In the intraoperative setting, the examination also needs to be tailored to the important surgical questions that must be answered for the proposed surgery. For example, if Fontan surgery is contemplated, evaluation of systemic and pulmonary venous drainage is paramount (Fig. 10.10, Video 10.8)

There are a number of other forms of complex congenital heart disease that—for one reason or another—fall under the “single ventricle” umbrella, even if they have two AV valves and two ventricles. In some patients, both ventricles are well-formed but other intracardiac features make a two ventricle repair unfeasible or undesirable, and therefore these patients are placed on a single ventricle pathway. Such complicating features include straddling/overriding AV valves, or double outlet RV with a VSD that is remote from either semilunar valve and makes two ventricle repair a high-risk proposition [48–50]. There are also some rare, complex cardiac defects that historically do not lend themselves well to a two ventricle repair. These include some forms of double outlet LV [51], superior-inferior ventricles with criss-cross AV relations [52, 53], etc. In many of these cases, there exist significant intracardiac abnormalities in addition to right or left ventricular hypoplasia.

When TEE is performed in patients with one of these complex cardiac lesions, a complete evaluation should be performed, with specific attention paid to AV valve size and orientation, ventricular chamber size and location of ventricular septal defect(s), and great artery relationships. In some cases, information from the TEE will be utilized to render an assessment as to whether a two ventricle repair is feasible. Currently, the bias for most clinicians caring for CHD patients is to perform a two ventricle repair whenever possible. However, the question as to whether a good one ventricle repair is better than a marginal two ventricle repair remains unanswered and is, in many instances, controversial [54–56].

With a single ventricle and single ventricle physiology, there is only one functioning pump that must serve both systemic and pulmonary circulations. Because of this, obligatory mixing of systemic and pulmonary blood flow occurs, resulting in systemic arterial hypoxemia. The eventual goal of surgical management of the single ventricle is to restore normal systemic arterial oxygenation by separating the circulations; this is performed by rerouting systemic venous (deoxygenated) blood directly into the pulmonary arteries, thereby bypassing the heart. Deoxygenated blood is expected to flow directly to the pulmonary arteries without the aid of a cardiac pumping chamber [57]. This is known as the Fontan procedure, which is named and based upon the original surgery described in 1971 by Fontan and Baudet for treatment of tricuspid atresia [58]. Over the past 40+ years the Fontan procedure has undergone a number of modifications and improvements, and has gained widespread acceptance as the preferred surgical management strategy for all forms of single ventricle [59]. It has been clearly established that, even without the aid of a right-sided pumping chamber, Fontan physiology is compatible with long-term survival and good functional status [60]. There are still a number of ongoing questions regarding long-term morbidity (arrhythmias, protein-losing enteropathy, liver dysfunction, ventricular dysfunction, plastic bronchitis, etc.) and survivability into late adulthood; these topics are beyond the scope of the current chapter but are fully discussed in many other references [59, 61–64].

While the ultimate goal for all single ventricle patients is the Fontan procedure and achievement of Fontan physiology, the complete Fontan operation cannot be performed in neonates or young infants because of a still immature pulmonary vascular bed, and still developing neonatal myocardium. The ideal timing for the Fontan procedure is generally felt to be after 2–3 years of age [65, 66]. Therefore, assuming single ventricle patients are correctly diagnosed in early infancy, almost all will require one or more staging surgeries prior to the Fontan procedure. The purpose of these staging surgeries is to ensure that patients are optimally prepared for their eventual Fontan procedure. For successful Fontan physiology, certain key anatomic and physiologic factors should ideally be present, including adequate size pulmonary arteries, low pulmonary arteriolar resistance, no more than mild AV valve regurgitation, and normal ventricular systolic and diastolic function [65, 66]. A full discussion of these important factors can be found in many references [59, 63, 67–70].

Different institutions utilize TEE to varying degrees for the various surgical procedures performed as part of single ventricle surgical pathway. Nonetheless, TEE can provide useful and important information. Preoperative evaluation of single ventricle patients by TEE is generally excellent due to its superior imaging capabilities. However, most preoperative single ventricle patients will have already undergone extensive imaging by several different modalities, hence TEE is used primarily as a complementary imaging technique, e.g. when assessment of AV valve function is desired in a larger patient with poor transthoracic imaging. For postoperative assessment, TEE can play a more prominent role. It is well known that postoperative single ventricle patients, particularly Fontan patients, are notoriously difficult to image by transthoracic echocardiography. Therefore TEE can provide a much greater contribution in the assessment of such patients, most notably in the immediate postoperative period. The following section discusses the important preoperative and postoperative features that can and should be assessed by TEE, whenever it is performed in single ventricle patients.