From October 1989 to 1991 May, 100 cases of open heart surgery were performed under the cardiopulmonary bypass. 1. There were 47 male and 53 female patients ranging in age from 2 months to 64 years. 2. Of 100 cases of open heart surgery, 65 cases were congenital heart diseases, and 35 cases were acquired heart diseases. 3. In 65 cases of congenital heart diseases, there were 60 cases[92 %] with acyanotic heart anomaly and 5 cases [8 %] with cyanotic heart anomaly. 4. Among the 42 patients less than 15 years of age, 21 patients[50%] were below 10 kg and the operative mortality was 0.05 %. 5. The overall mortality was 4 %, and the operative mortality of congenital and acquired heart disease was 3.1% and 5.6%.