Most patients with acute myocarditis manifest particular clinical signs and symptoms, including marked cardiac failure and/or a high degree of atrioventricular block on admission. However, a 78-year-old man did not have symptoms and was hospitalized as a result of abnormalities observed on an incidentally obtained electrocardiogram (ECG). Several days later, he developed cardiogenic shock and fulminant myocarditis, which required percutaneous cardiopulmonary support; however, the cardiac failure persisted and he died approximately 4 months later. The ECG showed findings similar to those of acute inferior myocardial infarction, and on left ventriculography, diffuse hypokinesis was observed most prominently in the inferoposterior wall. During autopsy, interstitial fibrosis was marked in the inferoposterior wall, with small, round, cell infiltration prominent at the same site. Clustering of these cells is a characteristic feature of chronic myocarditis.