['As patients began to survive for longer periods following modified Fontan operations (conventional atrio-pulmonary connection), the late morbidity after this procedure became increasingly apparent. The purpose of the present study was to evaluate late sequelae of modified Fontan operations in long-term survivors (n=14) at our institute.', 'The cohort consisted of patients who underwent a modified Fontan operation between 1981 and 1990. Thus, all patients were examined at least 10 years postoperatively in this study. Early mortality, within 30 days of the operation, was 17.6% (three of 17 patients died from low output syndrome). Excluding these early deaths, the cumulative survival rate at 5 and 10 years was 100 and 79%, respectively. Arrhythmias including atrial fibrillation or flutter were the main late causes of morbidity. The arrhythmia-free rate at 5 and 10 years was 77 and 50%, respectively. Although the quality of life was considered good because all patients (n=11) who survived for 10 years or more were in class I or II according to the New York Heart Association classification, most of them in fact suffered from potentially life-threatening arrhythmias.'] Does high frequency of arrhythmias after Fontan operation indicate earlier anticoagulant therapy?