Mostly of the sudden deaths, except in-hospital death and death within 48 hours of discharge, are declared in the emergency department by emergency physician. The purpose of this study is to review the protocol of cardiopulmonary resuscitation (CPR) in out-of-hospital cardiac arrest by understanding the cause of sudden death from autopsy results. A retrospective analysis was performed by 48 months of medical records from emergency department of a tertiary hospital. The analysis was made from the patient group which gone through autopsy in the main office of National Institute of Scientific Investigation. In the emergency department, 1913 patients were declared death and 43 patients have received autopsy and 19 (1.0%) were natural death. 14 partients received CPR in the natural death group, and 13 were specified as cardiovascular disease. Result of this study represents the importance of prehospital CPR in case of unexpected cardiac arrest patients. However to generalize this result, all dead patients must go through autopsies for medical purpose which the frequency alse should be increased.