Three infants, each with a clinical picture of dilated cardiomyopathy, underwent endomyocardial biopsy. Immunohistologic analysis revealed chronic myocarditis. In one infant, a postviral etiology of chronic myocarditis could be assessed on the basis of molecular techniques. Therapy with azathioprine and prednisone resulted in the normalization of echocardiographic findings. Based on these observations, a randomized, multicenter treatment study of chronic myocarditis in children (TCMC) has been initiated.