In order to evaluate the result of intraoperative TEE monitoring for cardiothoracic surgery, 113 patients were involved in this study. They included 65 males and 48 females, with an average age of 48.8 +/- 16.6 years, ranging from 10 to 74 years. The pre-operative diagnoses consisted of 41.6 per cent coronary artery disease, 34.5 per cent valvular disease, 12.4 per cent congenital heart disease, 8 per cent aortic aneurysm or aortic dissection, and 3.5 per cent of miscellaneous. The TEE appeared to provide accurate information by beating to changes in the left ventricular preload and contractility in all patients. The severity of valvular dysfunction, intracardiac air/mass, Swan Ganz catheter position, sites of congenital heart defect and aortic dissection were either assessed or reconfirmed during the operation. The ease of TEE technique was satisfactory, since unsuccessful attempt was observed in only 1.8 per cent. One patient died from rupture of thoracic aortic dissection which was related to TEE probe insertion. These data suggest the favorable result of intraoperative TEE as a valuable tool for monitoring in cardiothoracic surgery. Although the technique is simple, special precaution must be observed for patients suffering from acute aortic dissection.