A comprehensive transthoracic echocardiographic imaging is possible for most pediatric patients. However, for patients in whom accurate anatomical and physiological assessment is not possible, transesophageal echocardiography (TEE) provides a supplemental diagnostic modality. Imaging the left ventricular outflow tract and the aorta involves a complicated technique of rotation, flexion, and changes in the depth of the transesophageal probe because the areas of interrogation involve multiple planes within the thoracic cavity. Furthermore, the relationship between the esophagus and the cardiovascular structures changes at various levels of the thorax. Transesophageal probes having characteristics of frequency agility, all forms of Doppler capability, and a higher number of crystal elements are now available. Abnormalities of the subaortic area, the aortic valve, coronary arteries, and the entire thoracic aorta can be clearly demonstrated. TEE also has played a complementary role in diagnostic and interventional catheterization. It has become vital in the operating room for the preoperative definition of certain aspects of the anatomy and for immediate postoperative evaluation of the result of surgery. (ECHOCARDIOGRAPHY, Volume 13, July 1996)