Although the Fontan procedure is now being applied to younger patients, the influence of patients' age at the time of surgery on long-term results remains unclear. We investigated whether age at Fontan completion affects subsequent hemodynamics and exercise capacity in patients with a dominant left ventricle followed up for more than 5 years.Between January 1990 and December 2001, 68 patients with a dominant left ventricle underwent total cavopulmonary connection (TCPC) at our institute. The survivors routinely underwent postoperative exercise tests and catheterization at 1 year and then every 5 years after TCPC, and were divided into group A (<3 years; n = 32) and group B (≥3 years; n = 33), according to age at time of the Fontan procedure and retrospectively reviewed. We also examined the correlation between age at Fontan and data from postoperative catheterization or exercise tests.None of the patients died during a follow-up period of 91.2 ± 46.7 months. The postoperative exercise capacity (peak oxygen consumption; % of normal [61.3 ± 11.5 versus 51.9 ± 9.1, p = 0.0001]), cardiac index () at 5 years (3.31 ± 0.62 versus 2.86 ± 0.69, p = 0.0133) and at 10 years after TCPC (3.24 ± 0.46 versus 2.61 ± 0.65, p = 0.0194), and ventricular ejection fraction (%) at 10 years after TCPC (62.1 ± 7.6 versus 53.0 ± 8.0, p = 0.0131) were significantly higher in group A. Age at Fontan completion inversely correlated with postoperative peak oxygen consumption (R = −0.374, p = 0.0006) and cardiac index at 5 years (R = −0.452, p = 0.0003) and 10 years after TCPC (R = −0.491, p = 0.0072).Earlier TCPC is beneficial in the long term from the viewpoint of exercise capacity and hemodynamics among patients with a dominant left ventricle.