ABSTRACT: BACKGROUND: Patients with Senning repair for complete transposition of the great arteries (d-TGA) show an impaired exercise tolerance. Our aim was to investigate changes in exercise capacity in children, adolescents and adults with Senning operation. METHODS: Peak oxygen uptake (peak VO2), oxygen pulse and heart rate were assessed by cardiopulmonary exercise tests (CPET) and compared to normal values. Rates of change were calculated by linear regression analysis. Right ventricular (RV) function was assessed by echocardiography. RESULTS: Thirty-four patients (22 male) performed 3.5 (range 3--6) CPET with an interval of >= 6 months. Mean age at first assessment was 16.4 +/- 4.27 years. Follow-up period averaged 6.8 +/- 2 years. Exercise capacity was reduced (p<0.0005) and the decline of peak VO2 (-1.3 +/- 3.7 %/year; p=0.015) and peak oxygen pulse (-1.4 +/- 3.0 %/year; p=0.011) was larger than normal, especially before adulthood and in female patients (p<0.01). During adulthood, RV contractility changes were significantly correlated with the decline of peak oxygen pulse (r= -0.504; p=0.047). CONCLUSIONS: In patients with Senning operation for d-TGA, peak VO2 and peak oxygen pulse decrease faster with age compared to healthy controls. This decline is most obvious during childhood and adolescence, and suggests inability to increase stroke volume to the same extent as healthy peers during growth. Peak VO2 and peak oxygen pulse remain relatively stable during early adulthood. However, when RV contractility decreases, a faster decline in peak oxygen pulse is observed.