Regional left ventricular wall motion was assessed by two-dimensional echocardiography in 21 patients with complete transposition of the great arteries at a mean of 2.2 years (range 0.3 to 7) after an arterial switch operation. Fourteen patients had undergone a two-stage and seven patients a primary repair. Twenty patients were found to have echocardiographic images adequate for wall motion analysis. The results of these studies were correlated with thallium-201 myocardial perfusion scans. Left ventricular wall motion was assessed by measuring regional area change in parasternal and apical views. After planimetry of an end-systolic and an end-diastolic frame, the ventricle was divided into eight equal segments and the percent area change was calculated. Both a fixed reference and a floating system correcting for translation and rotation were applied. The measurements in the patient group were compared with normal age-matched values previously obtained in 55 normal infants and children. Wall motion abnormalities, found in seven patients, were located at the apex in three, at the inferior septum and anterolateral wall in one and the inferior, anterolateral and lateral walls in one patient each. All had a myocardial perfusion defect in a corresponding anatomic location. One patient with a small reversible perfusion defect at the basilar septum had normal regional wall motion. The sensitivity of detecting impairment of myocardial perfusion was 0.95. Wall motion abnormalities were found only in patients who had undergone a two-stage repair. Echocardiographic wall motion analysis can be used as a screening method to identify patients with suspected myocardial ischemia after the arterial switch operation.