EMB is recommended (Class 1) with Level B evidence in Clinical Scenarios 1 and 2 (Table 43.1). In these clinical scenarios, the aim of the EMB is to detect the more aggressive forms of myocarditis, such as giant cell myocarditis (GCM) and necrotizing eosinophilic myocarditis (NEM). Immunosuppressive treatment may improve the outcome in these forms; however, in the absence of clinical improvement, the diagnosis of GCM and NEM may require early implantation of mechanical circulation device support. Conversely, the diagnosis of lymphocytic myocarditis is a positive prognostic factor for spontaneous recovery, even in patients on inotropic or mechanical circulatory support.

EMB is considered reasonable (Class IIa) with Level C evidence in Clinical Scenario 3 because patients may be at risk of cardiac sarcoidosis or idiopathic granulomatosis myocarditis and in Clinical Scenario 4 because they might be at risk of hypersensitivity myocarditis (HSM) (Table 43.1). Both sarcoidosis and HSE may respond to therapy with corticosteroids.

EMB is also considered a reasonable procedure (Class IIa) with Level C evidence in cases of unexplained heart failure associated with suspected anthracycline cardiomyopathy (Clinical Scenario 5) or restrictive cardiomyopathy (Clinical Scenario 6) in which it may reveal either a specific infiltrative disorder, for example, amyloidosis or hemochromatosis, or myocardial fibrosis and myocyte hypertrophy consistent with idiopathic restrictive cardiomyopathy and in the setting of any unexplained cardiomyopathy in children (Clinical Scenario 8).

In cases of suspected cardiac tumour (Clinical Scenario 7), with the exception of typical myxomas, EMB is a reasonable investigation (Class IIa) with Level C evidence, if (1) the diagnosis cannot be established by noninvasive or less invasive techniques, (2) tissue diagnosis can be expected to influence the course of therapy, (3) the chances of successful biopsy are believed to be reasonably high and (4) the procedure is performed by an experienced operator [1].

EMB may be considered to detect a lymphocytic myocarditis in Clinical Scenario 9 (Class IIb), with Level B evidence and in Clinical Scenario 10, in unexplained hypertrophic cardiomyopathy, in suspected ARVD and unexplained ventricular arrhythmias (respectively, Clinical Scenarios 11,12,13) (Class IIb) with Level C evidence. EMB should not be performed in the setting of unexplained atrial fibrillation (Class III), with Level C evidence.