Myocarditis, often caused by an infectious agent, may have a presentation mimicking that of acute myocardial infarction. The authors describe a young man who, when first seen in the emergency department, appeared to have an acute myocardial infarction with normal coronary arteries. At autopsy, the histologic findings were diagnostic of active myocarditis, mixed-cell type. Neutrophilic infiltration with microabscess suggested an infectious cause, although the etiology was uncertain. The patient's clinical course, pathologic findings, and several treatment modalities are discussed. The differentiation between acute myocardial infarction and acute myocarditis can be difficult. Electrocardiographic changes and enzyme elevations are common in both. Therefore, clinicians should consider myocarditis in all patients--particularly young patients--with normal coronary arteries and suspected myocardial infarction.