A 69-year-old man underwent mitral valve replacement for suspected infective endocarditis and coronary artery bypass grafting with left internal thoracic artery and saphenous vein graft. During the period of coming off cardiopulmonary bypass, enlargement of the ascending aorta and bleeding from the suture line were observed. Intraoperative transesophageal echocardiography and direct epi-aortic echography revealed acute aortic dissection extending from the ascending aorta to the descending aorta. Replacement of the ascending aorta was performed under deep hypothermic circulatory arrest and continuous retrograde cerebral perfusion through the superior vena cava. The postoperative course was uneventful and he was discharged on postoperative day 41. Aortic dissection during cardiac operation is a rare but serious complication. Prompt recognition and appropriate surgical management are necessary to improve patient outcome.