The aim of this study was to evaluate the ability to recover from exercise in patients with a Mustard/Senning (M/S) repair for transposition of the great arteries and to identify the major determinants. A total of 40 consecutive patients with a M/S repair at a mean age of 10.0 +/- 9.8 months underwent maximal cardiopulmonary exercise testing at 19.5 +/- 11.3 years of age. Results were compared to those of a cohort of 153 healthy individuals. Decay of oxygen uptake (VO2), CO2 (VCO2), minute ventilation (VE), heart rate (HR) was calculated for the first minute of recovery. M/S patients had reduced peak VO2(22.9 +/- 7.2 vs 34.2 +/- 9.5 ml O2/kg/min, p < 0.0001) and VO2 slope (0.27 +/- 0.10 vs 0.47 +/- 0.2 L O2/min, p < 0.0001), Peak O2 pulse (p < 0.0001) and peak HR (p = 0.001) were reduced. VCO2 and VE slopes were reduced (p < 0.0001 for both), whereas HR slope was similar (p = 0.38). In M/S patients, the only independent determinants of VO2 slope during recovery were pulse O2 slope (p < 0.0001) and VCO2 slope (p < 0.0001). In M/S patients, a limited cardiopulmonary reserve affects not only maximal exercise responses but also the recovery phase. A prolonged recovery of O2 pulse and a prolonged CO2 retention with subsequent prolonged hyperpnea are the main determinants of the delayed recovery.