Thirty-one children with postoperative coarctation of the aorta underwent maximal graded bicycle ergometry using an electronically braked ergometer and the James protocol; 18 also underwent expiratory gas measurement using a mass spectrometer. Twenty-two age- and gender-matched normal subjects were used as a control group. The mean age at operation was 41 months and the mean age at evaluation was 134 months (mean follow-up interval 93 months). The original surgical repair was subclavian flap repair in 8 patients, end to end anastomosis in 21, patch aortoplasty in 1 patient and tubular graft in 1. Patients exercised until exhaustion and maximal exercise variables were obtained. The maximal voluntary peak heart rate was 183 beats/min (94.6% of predicted value), indicating excellent effort. Mean power was 111% of predicted value and, when measured, maximal oxygen consumption was 89% of predicted value with an anaerobic threshold at 63 +/- 3.5% of exercise time. The observed work variables were not different from values in the control group and were not affected by the type of repair. The mean peak systolic blood pressure was 152 +/- 7.6 mm Hg versus 147 +/- 5.7 mm Hg in the control group (p = NS). Patients who had associated intracardiac lesions had significantly lower maximal oxygen consumption (85 +/- 3% vs. 98 +/- 4% of predicted value). The results suggest that adequate cardiopulmonary function, normal or above average work capacity and normal exercise systolic blood pressure can be obtained in children with satisfactory repair of coarctation of the aorta performed before school age.