The authors developed a model that relates survival from myocardial infarction or cardiac arrest to four classes of interactive variables describing the rural community, the patient, Emergency Medical Service (EMS) system inputs, and EMS system process in caring for the suspected cardiac patient. Using data from 92 EMS systems in three geographically distinct and physically dissimilar regions, the authors found a consistent and significant relationship between the probability of patient survival and cardiac disease severity, age, sex, the presence of a life-threatening arrhythmia, health care resources available to the EMS system, citizen-initiated cardiopulmonary resuscitation, EMS response time, and the presence of a paramedic on the ambulance responding to the call. The model affords the opportunity to enumerate those factors with the greatest influence on cardiac survival within the community and to test expected increases in survival gained through incremental changes in these factors.