BACKGROUND AND OBJECTIVES: This study aimed to evaluate the usefulness of cardiopulmonary exercise test (CPET) in children with various congenital heart diseases (CHDs). SUBJECTS AND METHODS: Forty-eight children and adolescents (18 girls and 30 boys; mean+/-SD age, 12.6+/-0.5 years) with CHD who had undergone corrective surgery performed CPET using a programmable treadmill. The participants were divided into 4 groups based on the surgery performed: Fontan operation (12 patients), total correction for tetralogy of Fallot (13 patients), repair for coarctation of aorta (11 patients), and corrective surgery for simple CHDs (12 patients). Patients with simple CHDs who had undergone an early surgery were selected as controls. RESULTS: Progressive exercise time was the longest in the simple CHD group than in the other groups (10.6+/-2 versus 8.2-8.7 min, p=0.122). Absolute and predicted values of mean peak oxygen consumption were the lowest in the Fontan operation group (p=0.220 and 0.091, respectively). The coarctation of aorta group exhibited a prominent blood pressure response, that is, an elevation in the systolic blood pressure relative to that in the other groups at rest (131.7+/-18.8 versus 114.4-121.3 mmHg) and at peak exercise (196.5+/-41.5 versus 146.8-184.3 mmHg). CONCLUSION: CPET can be a useful tool to clarify the exercise capacity and reflect the hemodynamic status of patients who have undergone surgery for various CHDs and other heart diseases.