Midterm surgical results of arterial switch operation for transposition of the great arteries with intact septum. Between April 4, 1984, and December 31, 1987, 156 consecutive neonates with simple transposition of the great arteries underwent an arterial switch operation (ASO) at our institution. Surgery was performed before the age of 15 days in 96%, and patient weight was less than 3 kg in 28%. Seventeen patients (10.9%) died after surgery. One patient was lost to follow-up. Of the 138 survivors, two died of myocardial infarction 35 and 40 days, respectively, after surgery. They were the only late deaths, and actuarial survival rates were 87% (70% confidence level [CL], 83-89%) at 45 days and 87% (70% CL, 68-95%) at 52 months. Another patient had a myocardial infarction 50 days after surgery and is well 50 months later. Pulmonary stenosis was observed in 14 patients (10.3%) during the first year after surgery; two patients were reoperated on 10 and 12 months, respectively, after ASO. Aortic regurgitation was observed in 17 patients: two had grades II and III, respectively, aortic regurgitation on aortography; in 15 patients, it was detected only by Doppler examination. At the last follow-up (2-52 months after ASO; mean, 27.3 +/- 11.3 months), all patients were asymptomatic and taking no medication. On bidimensional echocardiography, left ventricular fractional shortening was normal at rest in all survivors but one. One patient had junctional rhythm, and one had Wenckebach periods; the remainder were in sinus rhythm. For as long as 5 years after ASO, late death and reintervention were rare; 99% of the survivors were asymptomatic and had sinus rhythm and good systemic ventricular function. 