A 22-year-old man presented with congestive heart failure following flulike symptoms. The diagnosis of acute myocarditis was confirmed by endomyocardial biopsy, which revealed mild infiltration of inflammatory cells. A favorable response to beta-adrenergic receptor blockade was seen, and the patient was discharged without symptoms. Five months later, however, congestive heart failure recurred, and intracardiac thrombi were demonstrated. The patient died after two months. Postmortem examination revealed left ventricular dilatation with slight interstitial fibrosis; the diagnosis was dilated cardiomyopathy. Thus, progression of biopsy-proven myocarditis to dilated cardiomyopathy 10 months after the onset of disease was documented.