Objective: To determine there is a subnormal exercise performance in children with non-operated ventricular septal defect and operated tetralogy of fallot compared to normal controls and 2) To determine physical activity is an important factor for lower exercise performance in these conditions. Design and Setting: Retrospective Study. The data were collected from the cardio pulmonary exercise testing and physical activity questionnaire at Department of Pediatrics Cardiology and Department of Cardiovascular Rehabilitation, U.Z. Hospital, Leuven, Belgium.