A procedure descried by Fontan and Baudet in 1971 successfully bypassed the right ventricle in Tricuspid Atresia patients, after then many modification of the Fontan operation had been described and applied to many cyanotic complex heart patients. Forty patients with a variety of cardiac malformation underwent the Fontan operation at Seoul National University hospital (September 1978 to June 1986). The age at operation ranged 2 months to 18 years. Each number of cases according to basic cardiac anomaly was as follows; 17 in Tricuspid Atresia, 17 in Univertricular Heart, 2 in Double outlet of Right Ventricle, 2 in Transposition of the Great Arteries and 2 in Criss-cross heart. Total mortality rate after the Fontan operation was 50%. There was only one late death (>30 days). Mortality rate under 4 years of age (67%) was higher than that between 4 and 18 years of age (40%). we observed a significantly higher mortality for patients who, in the immediate postoperative period, had central venous pressure greater than 25cm H2O. 45% among survivals did not require further medication. Although mortality rate after the Fontan operation is much higher than that in the foreign literature, operative mortality will decline with the increased expirence of surgeon and the effective patients selection.