Purpose .– Geometric profile of the left and right outlets as well as position and size of the ventricular septal defects (VSD) determine the surgical approach of malposition of the great vessels.

Aim .– To determine the ability of the 3D echocardiography (3DE) to depict the outlet chambers in normal and pathologic situations.

Methods .– Twenty patients were prospectively enrolled [10 had normal heart, five tetralogy of Fallot (TOF), three double outlet right ventricle (DORV), two double discordance (DD) with VSD]. The median age was 3.6 years (range 2 months–13 years). All underwent transthoracic 3DE (Philips, ie 33, X5-1 and X7-2). Full volume and Live 3D acquisition were performed. Off-line analysis was performed using a dedicated system (Qlab version 9). An asymmetry index of the VSD was calculated by the maximal 3D diameter divided by the minimal 3D diameter. A cut-off of 1.25 was set to distinguish ovale and circular shape.

Results .– Mitro-aortic continuity was observed in all controls and patients with TOF. Mitro-aortic distance was measured in patients with DORV (36 mm/m ² ). Septo-aortic and septo-pulmonary continuity was observed respectively in control and DD with VSD. Distance between tricuspid and pulmonary valve was (25.7 mm/m ² ) in control, (54.4 mm/m ² ) in TOF, (58.9 mm/m ² ) in DORV, and (17.5 mm/m ² ) in DD. VSD was in sub-aortic position in TOF and in 3 DORV; in sub-pulmonary position in two DD. Mean size of the VSD was 13.8 mm (27.3 mm/m ² ). Shape of the VSD was circular in all but one DD with small oval VSD; subvalvular insertion on VSD crest was observed in the same patient responsible of sub-pulmonary stenosis.

Conclusions .– 3DE is able to describe the outlet chambers and VSD position and geometry. This tool could help to determine the best surgical strategy in patients with malposition of the great vessels.