Objectives: Investigate the effects of left and right ventricular function and severity of pulmonary valve regurgitation, quantified by cardiac magnetic resonance (CMR), on exercise tolerance in adult patients who underwent ToF repair at a young age. Methods: This is a retrospective cohort study of 52 patients after ToF surgery and 33 age- and sex-matched healthy volunteers. CMR and cardiopulmonary exercise testing (CPET) were performed on all patients; CPET was performed on control subjects. Results: The main finding of CPET was a severe decrease in oxygen uptake at peak exercise VO2peak in TOF patients. The patients were characterized also by lower pulse O2peak and heart rate at peak exercise. Ejection fraction of the right and left ventricles was correlated (r = 0,32; p = 0,03). Left ventricle ejection fraction was negatively correlated with right ventricular volumes (r = −0,34; p = 0,01) and right ventricular mass (r = −046; p < 0,00). Right ventricular mass was positively correlated with left ventricular variables (left ventricle end diastolic volume, r = 0,43; p = 0,002; left ventricle end systolic volume, r = 0,54; p < 0,00) as was VO2peak: LVEDV (r = 0,38; p = 0,01); LVESV (r = 0,33; p = 0,03) and LV mass (r = 0,42; p = 0,006). Conclusion: Exercise intolerance in adults with repaired ToF is markedly depressed. The decreased exercise capacity is correlated with impaired RV function and may be associated also with LV dysfunction, which suggests right-to-left ventricular interaction.