This is a report of cardiac arrests which occurred in the operating room of National Medical Center from Jan. 1, 1970 to Dec. 31, 1976. All kinds of operations were performed in this hospital, butlopen heart surgery was excluded from this study. During this period 22, 825 surgical operations were done and 74 cardiac arrests occurred among them. Overall incidence of cardiac arrest was 1: 308 (0. 32%) and 43% of cardiac arrests were successfully resuseitated.