Background: The standard for door-to-balloon(d2b) time by the national emergency department information system is within 90 minutes, as recommended by ACC/AHA guidelines for ST-elevation myocardial infarction(STEMI). We aimed to evaluate the impact of the standardization of a "critical care protocol��� on the d2b time for STEMI patient management. Methods: We analyzed consecutive patients presenting with STEMI from Jan 2008 to Jun 2009. In Jan 2009, a standardized critical care protocol went into effect. During first 12 months, an emergency department(ED) or internal medicine doctors called cardiologists when STEMI patients visited the ED. Percutaneous coronary intervention(PCI) team was activated after the decision of the cardiologist. Since Jan 2009, however, the ED or internal medicine doctors were empowered to initiate the ���critical care protocol��� that activates the paging system notifying the PCI team members and administered the standardized medications. Subjects were patients presenting with STEMI and within 12 hours after symptom and who were treated with primary PCI. Results: A total of 115 patients were included in this study; 67 were treated before implementation of the protocol and 48 treated after implementation of the protocol. Mean age, sex, risk factors except smoking, and Killip class were similar in both groups. Implementation of the critical care protocol reduced the median d2b time 55 minutes (from 133 to 78 minutes; P <0.001) and increased the proportion of patients undergoing the primary PCI within 90 minutes from 15% to 73% (Figure). Conclusion: We demonstrate that the standardization of a critical care protocol for STEMI patients reduces the d2b time and increases the proportion of patients undergoing PCI within 90 minutes.