Exercise tolerance time and cardiac output (Q) measures during peak exercise were examined in 8 children with repaired congenital heart defects to determine the effects of physical training. Children ranged in age from 4.5 to 15 years (mean age 8.5). The children had undergone the following surgical repairs: Mustard operation for d‐trans‐position of the great arteries (n = 3); mitral valve replacement (n= 1); tetralogy of Fallot (n = 2); and Fontan operation (n= 2). Subjects participated in a 24‐session, 12‐week, one‐hour session hospital‐based aerobic exercise program of graduated intensity and duration. Work loads of 60, 70 and 80% of maximal heart rate were utilized. Graded exercise testing on a treadmill was performed prior to and following the training program. Pre and post values of Q were obtained via the acetylene rebreathing method. Exercise tolerance time increased significantly from 9.4 to 10.9 minutes (p<.01). Following training, peak exercise values of Q significantly increased from 4.91 to 6.05 L/min (p<.01). There were no complications. These data indicate that a monitored aerobic exercise program can increase exercise tolerance time and cardiac output values in children following corrective surgery for congenital cardiac defects.