Background : The purpose of this study is to investigate the influencing factors on the length of emergency department stay of patients with acute myocardial infraction. Methods : we reviewed medical records of all patients who were Hospitalized with acute myocardial infraction from March 1, 2002 to February 28, 2003. Results : The average length of stay in the emergency room of the subjects was 182.74 minutes. After the emergency room treatment, 48.1% of the subjects were transferred to intensive care unit. The hospitalization through emergency room mostly took place in the office hours. There were more patients on Monday. The influencing factors on the length of stay in the emergency room of patients with acute myocardial infraction were emergency room arrival time which was classified in seasons, treatment hours of specialized doctors, medical care insurance and required time of radiologic examination. Conclusion : In order to reduce the length of emergency room stay, it might be an available solution secure enough spaces, facility, and staff of the radiologic test only for the patients of the emergency room. And the effective use of emergency facility and space, establishment of standardized treatment guideline, and provision of emergency treatment support system are also needed.