In brief Physical activity can lead to sudden death in a patient who has viral myocarditis. Vigilance is required in its detection because it is not only serious, but also rare and difficult to diagnose, given that its signs and symptoms are nonspecific. The diagnosis requires confirmation by biopsy. The natural history is highly variable; patients may develop early or late severe congestive heart failure. Treatment consists of conventional heart failure therapy including angiotensin converting enzyme (ACE) inhibitors, diuretics, and digitalis. Corticosteroid therapy seems to provide no added benefit, but should not be withheld in cases of extreme left ventricular dysfunction. Exercise restrictions are important during the acute phase, and exercise testing helps guide a safe return to activity.