The incidence of myocarditis in endomyocardial biopsy samples from patients with congestive heart failure. We present the combined experience of three Yugoslavian cardiovascular centers in the application of endomyocardial biopsy for the diagnosis of myocarditis in patients who present clinically with congestive heart failure. The study group comprised 107 patients (mean age, 40.8 years; range, 19 to 61 years). On the basis of patient history and diagnostic tests, the following clinical diagnoses were established: dilated cardiomyopathy (85), myocarditis (16), and alcohol-induced heart disease (6). EMB samples were taken from the left ventricle (95) or both ventricles (12) by use of a King's College bioptome, with a mean of 3.2 samples per patient. Histologic evidence of myocarditis was noted in 10 of 85 patients (12%) with a clinical diagnosis of dilated cardiomyopathy, in 2 of 6 patients (33%) with alcohol-induced heart disease, and in 12 of 16 patients (75%) with a clinical diagnosis of myocarditis. There was confirmation of the clinically suspected diagnosis in 63% of cases, a change of diagnosis based on histology in 15% of cases, and nonspecific findings in 22%. However, useful information was obtained in 78% of the cases, and there was a 22% incidence of histologically proven myocarditis for the entire group. Our results indicate that endomyocardial biopsy is beneficial in determining the true incidence of myocarditis in patients with a clinical presentation of dilated cardiomyopathy. 