Abstract OBJECTIVES We sought to determine if early ventricular volume unloading improves aerobic capacity in patients with single ventricle Fontan physiology. BACKGROUND Surgical strategies for patients with single ventricle include intermediate staging or early Fontan completion to reduce the adverse affects of prolonged ventricular volume load. The impact of this strategy on exercise performance has not been evaluated. METHODS Retrospectively, we reviewed the exercise stress test results of all preadolescents with single ventricle Fontan physiology. “Volume unloading” was considered to have occurred at the time of bidirectional cavopulmonary anastomosis or at the time of Fontan surgery in those patients who did not undergo intermediate staging. Potential predictors of aerobic capacity were analyzed using multivariate regression. RESULTS The patients (n = 46) achieved a mean percentage predicted of maximal oxygen consumption (V̇O 2max) of 76.1% ± 21.1%. The mean age at the time of volume unloading was 2.7 ± 2.4 years, and the mean age at testing was 8.7 ± 2 years. Intermediate staging was performed in 16 of 46 patients (35%). In multivariate analysis, younger age at volume unloading was associated with increased aerobic capacity (p = 0.003). Other variables were not predictive. The subgroup of patients who underwent volume unloading before two years of age achieved a mean percentage predicted V̇O 2max of 88.6% ± 24.1%. CONCLUSIONS Preadolescents with single ventricle who undergo volume unloading surgery at an early age demonstrate superior aerobic capacity compared with those whose surgery is delayed until a later age.