One hundred cases of open heart surgery were done at this Department in 1977. There were 65 congenital anomaly and 35 acquired diseases. Out of 65 cases of congenital malformation 35 acyanotic and 30 cyanotic cases were found. Fifteen cases of ventricular septal defect and 29 tetralogy of Fallot were noted eight patients expired out of 65 congenital anomaly [12.3%] , 4 out of 35 acyanotic [11. 4%] and 4 among 30 cyanotic anomaly[13.3%]. Among 35 cases of acquired heart disease 3 atrial myxoma [2 left and one right] and 32 valvular lesions were noted. In two cases open mitral commissurotomy, and in 30 valve replacement were done. Twenty-two single valve and 8 double valve replacement were done. Seven patients expired out of 30 patients [23.3%]. Among 22 single valve replacement cases 2 and among 8 double valve 5 died. ~ In eighteen mitral valve replacement cases 2 deaths occurred. One mitral insufficiency patient who expired suffered from severe pulmonary` hypertension [PA=120/67mmHg], tricuspid insufficiency and a large ventricular septal defect. The patient underwent mitral valve replacement, tricuspid annuloplasty and patch closure of ventricular septal defect. Over all mortality rate for 100 open heart surgery cases was 15%. Since 1977 open heart surgery cases were done routinely in this institution and cases are increasing rapidly. With present rapid improvement of economical status and introduction of medical insurance system, open heart surgery will be firmly established in Korea in the very near future.[KTCS 1978;2:213-226]