Intraoperative transesophageal echocardiography was compared with epicardial echocardiography after ventricular septal defect repair. This comparison was made in 18 children aged 7 to 137 months (median, 32 months), weighing 6.3 to 49.1 kg (median, 10.8 kg) from November 1989 to January 1991. Ventricular septal defect types were perimembranous (six), malalignment (seven), supracristal (three), midmuscular (one), and inlet (one). Eight children had isolated ventricular septal defects, four had tetralogy of Fallot, three had double outlet right ventricle, two had double chambered right ventricle, and one had pulmonary stenosis. Patch interrogation was complete in 17 of 18 transesophageal echocardiography and 16 of 18 epicardial echocardiography studies. Inability to fully interrogate the ventricular septal defect patch by epicardial echocardiography occurred in two children as a result of anterior ventricular septal defect location, limited epicardial exposure, and surgical hardware interference. Incomplete transesophageal echocardiography patch interrogation occurred in the child with the midmuscular ventricular septal defect. Seven residual ventricular septal defects were documented by color flow Doppler in six patients. Five of seven residual defects were demonstrated by both real-time transesophageal echocardiography and epicardial echocardiography imaging. Transesophageal echocardiography and epicardial echocardiography missed 1 and 7 defects, respectively. The missed defects were different with each technique and were confirmed by postoperative surface echocardiography. No residual defects of sufficient size to require reoperation were found as determined by combination color flow jet analysis and intraoperative oximetry (no pulmonary to systemic flow ratio was greater than 1.50). Patches caused two-dimensional and Doppler signal masking, but this was not limiting because all residual defects were found at the margins of the ventricular septal defect patch.(ABSTRACT TRUNCATED AT 250 WORDS)