Aortic dissection is a rare but devastating complication of cardiac operations. The purpose of this investigation was to assess the occurrence of aortic dissection during elective cardiac operations and the usefulness of intraoperative transesophageal echocardiography for the diagnosis and management of this complication. Data of consecutive adult patients undergoing elective cardiac surgery with transesophageal echocardiographic monitoring during an 8-year period were studied retrospectively. Aortic dissection was identified in 7 (0.13%) of 5,247 patients, and diagnosed immediately by transesophageal echocardiography in 5 of them; 2 were diagnosed later by transesophageal echocardiography. All aortic dissections were type A and they occurred after completion of the primary procedure. Two patients treated conservatively died within 5 days. Four of the 5 patients who underwent immediate reoperation survived with serious postoperative complications. Transesophageal echocardiography should be carried out when there is a risk of aortic dissection during cardiac operations, especially in the posterior wall of the ascending aorta, to avoid missing the diagnosis and delaying treatment.