Objectives In patients with univentricular heart disease, the total cavopulmonary connection (TCPC) is the preferred treatment. TCPC can be performed using the intra-atrial lateral tunnel (ILT) or extracardiac conduit (ECC) technique. The purpose of the present study was to evaluate exercise capacity in contemporary TCPC patients and compare the results between the 2 techniques. Methods A total of 101 TCPC patients (ILT, n = 42; ECC, n = 59; age, 12.2 ± 2.6 years; age at TCPC completion, 3.2 ± 1.1 years) underwent cardiopulmonary exercise testing. The patients were recruited prospectively from 5 tertiary referral centers. Results For the entire group, the mean peak oxygen uptake was 74% ± 14%, peak heart rate was 90% ± 8%, peak workload was 62% ± 13%, and slope of ventilation versus carbon dioxide elimination (VE/VCO2 slope) was 127% ± 30% of the predicted value. For the ILT and ECC groups, patient age, age at TCPC completion, body surface area, peak workload, and peak heart rate were comparable. The percentage of predicted peak oxygen uptake was lower in the ILT group (70% ± 12% vs 77% ± 15%; P = .040), and the percentage of predicted VE/VCO2 slope was greater in the ILT group (123% ± 36% vs 108% ± 14%; P = .015). In a subgroup analysis that excluded ILT patients with baffle leak, these differences were not statistically significant. Conclusions Common exercise parameters were impaired in contemporary Fontan patients. Chronotropic incompetence was uncommon. The peak oxygen uptake and VE/VCO2 slope were less favorable in ILT patients, likely related to baffle leaks in some ILT patients. These results have shown that a reduced exercise capacity in Fontan patients remains an important issue in contemporary cohorts. The ECC had a more favorable exercise outcome at medium-term follow-up.