An aquarium-housed, 6-mo-old African penguin (Spheniscus demersus) presented with acute respiratory distress. Auscultation revealed a grade II–III systolic murmur in the absence of adventitial sounds, and an enlarged heart without pulmonary edema was seen radiographically. Echocardiographic evaluation revealed atrioventricular (AV) valvular dysplasia and ventricular enlargement. The penguin was treated with enalapril, furosemide, and pimobendan but died within 3 wk of detection of the murmur. Congenital dysplasia of the right AV valve with right atrial and ventricular dilation and ventricular hypertrophy were diagnosed on postmortem examination.