ObjectiveThe aim of this study was to evaluate the effects of a standardized exercise program on sports enjoyment and leisure-time spending in adolescents with congenital heart disease and to know what the moderating impact of their baseline health behavior and disease knowledge is. MethodsIncluded were 93 patients, aged 10 to 25, with surgical repair for tetralogy of Fallot or with a Fontan circulation for single-ventricle physiology, of 5 participating centers of pediatric cardiology in The Netherlands. They were randomly allocated, stratified for age, gender, and type of congenital heart disease to a 12-week period with either: (1) three times per week standardized exercise training or (2) care as usual (randomization ratio 2:1). At baseline and after 12 weeks, participants completed Web-based questionnaires and were interviewed by phone. Outcome MeasuresPrimary analyses tested changes from baseline to follow-up in sports enjoyment and leisure-time spending in the exercise group vs. control group. Secondary analyses concerned the moderating influence of baseline health behavior and disease knowledge on changes from baseline to follow-up, and comparison with normative data. ResultsAt follow-up, the exercise group reported a decrease in passive leisure-time spending (watching television and computer usage) compared with controls. Exercise training had no effect on sports enjoyment and active leisure-time spending. Disease knowledge had a moderating effect on improvement in sports enjoyment, whereas health behavior did not. Compared with normative data, patients obtained similar leisure time scores and lower frequencies as to drinking alcohol and smoking. ConclusionsExercise training decreased passive, but not active, leisure-time spending. It did not influence sports enjoyment.