Abstract
Left atrioventricular valve aneurysm is a rare condition. Here we present a rare case of partial atrioventricular septal defect with an extremely thin left atrioventricular valve aneurysm mimicking valve perforation. Preoperative echocardiography demonstrated severe left sided atrioventricular valve regurgitation on the "cleft" and leaflet perforation. But we discovered a left sided atrioventricular valve aneurysm instead of a valve perforation. The "cleft" edge and the aneurysm were closed.