The arterial switch procedure has become an accepted reparative technique for transposition of the great arteries with or without ventricular septal defect. In this study the accuracy of prospective noninvasive imaging in detecting arterial tract obstruction and the prevalence and severity of arterial valvular regurgitation (as assessed by Doppler ultrasound) were evaluated in survivors of arterial repair. All 53 study patients underwent two-dimensional echocardiographic examination 2 days to 20 months (median 7 months) postoperatively; 43 patients also had pulsed and continuous wave Doppler studies. The accuracy of the noninvasive evaluation of arterial tract obstruction was determined by comparison of Doppler maximal instantaneous gradients with peak to peak gradients at nonsimultaneous catheterization in 26 patients. Twenty-one (81%) of the 26 patients underwent catheterization and successful pulsed and continuous wave Doppler examination of the right heart; 17 (81%) of these 21 had a maximal pressure gradient within 20 mm Hg of the peak to peak gradient obtained at catheterization. Echocardiographic identification of the stenotic site was correct in all eight of the patients in this group requiring reoperation. Twenty-three (88%) of the 26 patients who underwent catheterization had successful Doppler interrogation of the aortic tract; 22 (96%) of these 23 had a maximal instantaneous gradient within 20 mm Hg of the peak to peak catheterization gradient. Fourteen (32%) of 43 patients had mild or moderate pulmonary regurgitation by Doppler study. Three (7%) of the 43 had mild aortic regurgitation.