Primary arterial switch operation in neonates for repair of transposition of the great arteries with an intact ventricular septum or with a ventricular septal defect has become the operation of choice in our institution. By now, the surgical risk has been decreased to approximately 2 per cent. Early in our experience, postoperative supravalvar pulmonary stenosis was the only late hemodynamic complication of significance. Postoperative left ventricular function, including echocardiographic indices of left ventricular function, including echocardiographic indices of left ventricular systolic and diastolic function, have been within normal range in all patients. Almost all patients are in sinus rhythm as late as 6 years of the operation. It is our contention that primary arterial switch operation in infants with transposition of the great arteries results in improved left ventricular performance; the potential hazard of late coronary insufficiency and of aortic valve dysfunction requires continued monitoring of these patients.