During the period of June 1976 October 1980 131 cases of Open heart Surgery was performed at the National Medical Center in Seoul under the extracorpocal circulation. 77 cases were congenital heart disease and 54 were acquired heart disease. The age of the patients ranged between 2$frac{1}{2}$ and 51 years. For all patients partial hemodilution technique and moderte hypothermia was used during extracorporeal circulation and cardioplegia was done for myocardial protection since April 1978. 41 of congenital cases were non-cyanotic group and 1 case died. 36 of congenital cases were cyanotic group and revealed very high mortiality rate (16 death, 39%). 53 of acquired cases were cases of valvular heart disease, 34 mitral (3 death), 1 aortic, 4 mitral with aortic 12 mitral with tricuspid (3 death), 2 triple valves (2 death), and revealed mortality rate of 15.1% (8 death). 1 of acquired cases were left atrial myxoma. There were 25 cases of operative death and over all motality rate was 19.1%.