By comparison with adults, cardiopulmonary exercise testing in children with Tetralogy of Fallot is limited, and its clinical application less clarified. This study provides a comprehensive CPET profile in a child-adolescent population with repaired TOF, explores mechanisms underpinning exercise intolerance and associations with clinical outcome. Seventy-four CPETs were completed in 58 child-adolescents with rTOF (age 13.8 SD 2.4 years). CPET parameters were corrected for age, sex and body size. At follow-up (4.9 years, IQR 3.5-7.9) clinical status and re-intervention was evaluated and CPET indices predicting these outcomes determined. Cohort peak V̇O