A loud third heart sound and asymptomatic myocarditis during Mycoplasma pneumoniae infection.

A 20-year-old man had a fever and cough due to Mycoplasma pneumoniae pneumonia. He had no heart symptoms, but auscultation revealed an exceptionally loud third heart sound, suggesting cardiac involvement. Marked myocardial enzyme release, serial electrocardiographic ST-T changes, and transient increase in interventricular thickness and inferior wall hypokinesis at echocardiography supported the diagnosis of acute infectious myocarditis. Recovery was quick. This case shows that acute myocarditis with significant myocardial injury may pass without any subjective heart symptoms.