Left ventricular contractile function was compared between primary and two-stage arterial switch operation (ASO) in neonates and infants with simple transposition of the great arteries (TGA). Eight patients (group 1) underwent primary ASO at 13-42 (23 +/- 10 [mean +/- SD]) days of age, and five patients (group 2) underwent two-stage ASO after pulmonary artery banding and Blalock-Taussig shunting at 11-26 (15 +/- 3) months of age. Postoperative echocardiographic studies were undertaken at 6-48 (22 +/- 16) months of age in group 1 and 25-45 (32 +/- 7) months of age in group 2. The results were compared with those obtained from nine age-matched normal children (group N). To compare left ventricular contractile state among the patients, the deviations from the mean normal values in relations of end-systolic wall stress to fractional shortening and to rate-adjusted mean velocity of circumferential shortening (the stress-shortening index and stress-velocity index, respectively) were obtained for each patient. The stress-shortening index was significantly lower in group 2 (-3.1 +/- 3.1) than in group 1 (1.3 +/- 1.7, p less than 0.05); the stress-velocity index was significantly lower in group 2 (-3.3 +/- 1.8) than in group 1 (1.5 +/- 1.6, p less than 0.01) or in group N (-0.4 +/- 0.5, p less than 0.05). These results suggest that postoperative left ventricular contractility can be well preserved in patients after primary ASO for simple TGA in neonates, but there is a possibility of depressed contractility in patients after two-stage ASO.