BACKGROUND Ventricular function and arrhythmia in patients with Fontan circulation in long-term follow-up are still unknown. METHODS We retrospectively reviewed 48 patients who survived and were followed up for more than 15 years, among 110 patients who underwent Fontan operation in our institute from 1979 to 1992. Atriopulmonary connection was performed in 26 patients and total cavopulmonary connection in 22. The patients were categorized into right ventricle, left ventricle, and biventricle groups. Follow-up cardiac catheterization and exercise test were performed routinely every 5 years post surgery. Median age at Fontan operation was 5 years. RESULTS Mean follow-up was 18.5 years. Cardiac index in the total cavopulmonary connection group was higher than in the atriopulmonary connection group at 10 and 15 years post surgery (p<0.05). Ejection fraction in the left-ventricle group was higher than in the right-ventricle group. End-diastolic volume at 5, 10, and 15 years was significantly lower than at 1 year (p<0.05). End-diastolic pressure at 10 years was significantly higher than at 1 and 5 years (p<0.05). Beyond 15 years, 6 patients developed ventricular tachycardia. The only significant risk factors for the onset of ventricular tachycardia in a multivariate analysis were age at Fontan operation and absolute age (p<0.05). CONCLUSIONS Long-term follow-up of patients demonstrated that postoperative ventricular systolic performance seemed to become steady. Ventricular tachycardia was detected 15 years post surgery, especially in older patients with older age at Fontan operation, possibly revealing a risk factor in the long-term postoperative period, thereby meriting further consideration.