A 37-year-old woman was admitted with an acute anterior myocardial infarction. Coronary arteriography revealed a dissecting aneurysm of the left main coronary artery. The patient died from perioperative myocardial infarction following aortocoronary bypass surgery on the 102nd hospital day. Histologic sections of the aneurysm revealed that granulation tissue had replaced the aneurysm, suggesting spontaneous healing of the dissecting aneurysm.