From May 1977 to November 1993, 1, 500 cases of open heart surgery were performed under the cardiopulmonary bypass. In 1500 cases of open heart surgery 975 cases[65%] were congenital heart disease and 525 cases[35%] were acquired heart disease. In 975 cases of congenital heart disease, there were 812 cases[83%] of acyanotic congenital heart anomaly and 163 cases of cyanotic congenital anomaly. In 525 cases of acquired heart disease, most cases were valvular heart disease in which 557 valves were implanted. The each operative mortality of congenital and acquired disease was 7.7% and 7.4% respectively and then overall mortality rate was 7.6%. There has been increasing incidence of open heart surgery in infants in recent years. After 1990, 28 cases of infant open heart surgery below the 12month were performed. Most lowest weight was 2, 200g[15 days]. Operative mortality of open heart surgery in infant with weight below the 10kg was very high as a 25.7%.