The feasibility and potential adverse effects of using intraoperative transesophageal echocardiography (TEE) in 19 children ages 7.5 to 16 years undergoing surgical repair of a variety of congenital heart defects were evaluated. The ability of TEE to assess the adequacy of surgical repair as well as left ventricular function and wall motion abnormalities in this setting was also examined. Intraoperative transesophageal 2-dimensional and Doppler evaluation, and, in selected patients, echo-contrast and color flow imaging, were performed with either a 3.5- or 5.0-MHz phased array probe mounted within the tip of a flexible gastroscope. Probe insertion was successful in 18 of 19 patients. Fiberoptic endoscopy (9 patients) and autopsy (1 patient--cardiac donor) performed within 24 hours of surgery demonstrated no significant esophageal abnormalities. Intraoperative wall motion abnormalities were identified in 8 patients but did not persist after the operation. An adequate surgical repair was demonstrated by contrast and color flow imaging in most patients. Microcavitation was detected in 6 patients for greater than 5 minutes after a standard debubbling procedure. No patient displayed any adverse neurologic effects. It is concluded that, with the currently available probes, intraoperative TEE can be performed safely and reliably in children as young as 7.5 years of age. The procedure provides valuable information regarding wall motion abnormalities, cardiac function and the adequacy of surgical repair.