ABSTRACT Nearly 28 million prehospital emergency medical services (EMS) ambulances runs occur annually for patients with cardiovascular emergencies. The American Heart Association recognizes the value of EMS in the Chain of Survival yet the inclusion of EMS necessitates logistically challenging communication amongst multiple organizations. Often, prehospital providers are unaware of their own practice patterns and patient outcomes wasting valuable opportunities to learn from experience while inadvertently reinforcing suboptimal care. Providing feedback on clinical practice and patient outcomes is a simple and effective intervention that has been challenging to scale. We will use human factors engineering principles (user-centered design) to develop, refine, and implement a scalable feedback system we call “PORTAL.” PORTAL uses automated audit and feedback, non-financial incentives, and local champions to examine the impact on provider behavior through the performance of guideline compliant care in the setting of cardiovascular emergencies. This application describes a mixed-methods proposal that addresses major NHLBI priorities to improve patient health through the development and refinement of the PORTAL feedback system for EMS providers delivering acute cardiovascular emergency care to patients with chest pain. The Specific Aims are: 1) Examine the determinants of guideline compliance amongst EMS providers and stakeholders; 2) Refine the visual interface for automated EMS feedback through user-centered design; and 3) Examine the feasibility and refine the implementation of the PORTAL intervention to support a subsequent trial testing the effectiveness of the feedback intervention. The team is uniquely qualified to accomplish these Aims, with expertise in care transitions, healthcare operations research, biomedical informatics, human factors engineering, implementation science, pragmatic trial design, qualitative methods, and acute care medicine. The institutional environment at Vanderbilt University Medical Center is outstanding, including the Center for Clinical Quality and Implementation Research (CCQIR), nationally ranked graduate programs in the relevant fields of study; and the national CTSA coordinating center. This application will develop an automated feedback system for prehospital providers treating patients with suspected cardiovascular emergencies. Taking a user-centered approach by placing the EMS provider at the center of the design process will substantially advance the ability to enhance provider activities through the delivery of scalable feedback using provider and stakeholder input. Advancing the delivery of prehospital provider feedback creates a mechanism to improve the quality and safety of prehospital care through the enhanced uptake of guideline compliant care. We propose this work in preparation for a cluster randomized trial evaluating the impact on provider behavior and patient outcomes.