In 1979 during the period of about 10 months 320 cases of open heart surgery were done in Seoul National University Hospital. There were 220 Congenital anomaly cases consisting of 113 acyanotic and 107 cyanotic varieties, and 1 O0 acquired cardiac lesions. Out of 100 acquired lesions 96 were valvular cues. Among 97 valve replacement cases 3 were Ebstein anomaly treated with plication and tricuspid valve replacement. Operative mortality rate for congenital anomaly was 10.6%, with 2.7% for acyanotic and 22.4% for cyanotic group. For acquired lesions over all operative mortality was 7%. Tetralogy of Fallot, ventricular septal defect, and atrial septal defect were the 3 main congenital anomalies, with 88 cues, 69 cases, and 27 cues respectively. In 61 simple ventricular septal defect without other anomalies operative mortality rate was 1.6%, in 27 atrial septal defect no death and, in tetralogy of Fallot 12.2%. Among 69 ventricular septal defect cases 19[27.5%] type I VSDs, after Kirklin-Becu classification, were found, rather high relative incidence of type I compared with Caucasian patients. Among 97 valve replacement cases 20 double valves were replaced-11 mitral with aortic and 9 mitral with tricuspid valves. Over all operative mortality rate for valve replacement was 8.2% with 3.3% in 61 mitral valve replace-merit. The over all operative mortality rate for 320 open heart surgery cases was 10.6%. Bubble type oxygenator and xenograft bioprosthetic valves were utilized In almost all cases.[KTCS 1980;1:1-12]