Purpose: Prompt reperfusion therapy by means of primary percutaneous coronary intervention is an effective method for treating patients with ST-segment elevation myocardial infarction (STEMI). According to the ACC/AHA guidelines for these patients, the interval between arrival at the hospital and intracoronary balloon inflation (door-to-balloon time) should be 90 minutes or less. The aim of this study was to evaluate the effect of establishing an ECG transmission system and communication procedure in the emergency department (ED) to minimize door-to-balloon time for STEMI patients. Methods: We established both the out-of hospital and inhospital aspects of the ECG transmission system. Before patient arrival at our ED, we would attempt to receive initial ECGs from the referring hospitals via fax. In ideal cases, ECG findings were immediately reported to interventional cardiologists by the referring primary ED physician. Door-toballoon time segments were analyzed in a retrospective manner. We compared the effectiveness in minimizing reperfusion time between the use of inter-hospital 12-lead ECG transmission before patient arrival, and direct communication between emergency physicians and attending interventional cardiologists. Results: Of the total 142 STEMI patients who received percutaneous coronary intervention (PCI) during the study period, 112 (78.9%) received PCI within 90 min. The mean door-toballoon time of the 27 patients admitted with a pre-arrival 12- lead ECG transmission was significantly less than the others. Conclusion: Establishing both out-of hospital and in hospital strategies to reduce door-to-balloon time in patients with STEMI, by using pre-arrival ECG transmission and direct communication between emergency physicians and interventional cardiologists, is an effective approach to minimize time to reperfusion.