This study was undertaken to test whether multiplane transesophageal echocardiography (TEE) offers advantages in comparison with biplane TEE in the intraoperative monitoring during cardiac surgery. A diagnostic multiplane TEE was performed in 400 patients in the immediate preoperative and postoperative periods. We systematically acquired cardiac images from the gastric fundus, lower esophagus, and upper esophagus; complete views of the descending aorta were also recorded. Usefulness of the different views in providing essential additional clinical information compared with exclusive transverse (0 to 20 degrees) and longitudinal (70 to 110 degrees) planes of the biplane TTE was assessed assuming that with manipulation of a biplane probe, a 20 degrees are could be added to the conventional horizontal and vertical planes. A high success rate of each view was demonstrated; anatomy and pathologic condition were best visualized in oblique planes. The method proved to be particularly useful in the preoperative and postoperative phases of aortic dissection (27 cases), aortic (65 cases) and mitral (35 cases) valve replacement, mitral valve repair (38 cases), left ventricular aneurysmectomy (25 cases), bleeding from proximal suture of an aortic heterograft (2 cases), and positioning of left ventricular hemopump (2 cases). Additional regional wall motion abnormalities of the right (four cases) and left ventricle (six cases) not appreciated in 0 to 20 degrees or 70 to 110 degrees planes were detected. Multiplane TEE is a useful clinical tool during intraoperative monitoring of cardiac surgery. Most structures of the heart and great vessels lie on oblique planes, while other views are optimized with the aid of slight angle corrections. This method improves the evaluation of anatomy and pathologic condition of the heart and great vessels, of native and prosthetic valves, and of left and right ventricular function.