Pre- and postoperative exercise tests were performed on 12 children with severe congenital heart disease (CHD) (age, 4-12 years). Oxygen uptake, blood pressure, and heart rate responses to exercise were measured. Exercise test time and the tolerable speed of the treadmill increased significantly after the operation. When pre- and postoperative values were compared, exercise heart rates did not change in most of the children, while delta systolic blood pressure rose significantly. The significant increase in peak oxygen consumption (VO2/Kg) values also revealed that there was an improvement in their exercise capacity after the operation.