Survival after out-of-hospital cardiac arrest was studied in a suburban community (population 304000) before and after addition of paramedic services. During period 1 emergency medical technicians provided basic emergency care (cardiopulmonary resuscitation at the scene of collapse and during the journey to hospital). In period 2 additional care was given at the scene of collapse by paramedics capable of advanced emergency care (defibrillation, endotracheal intubation, drugs). During the 3-yr study 585 patients with cardiac arrest caused by heart disease received prehospital emergency resuscitation. Paramedic services improved the rate of live admission to the coronary-care or intensive-care unit from 19% to 34% (p less than 0.001) and the rate of discharge from 7% to 17% (p less than 0.01). The mean time from collapse to delivery of advanced emergency care was 27.5 min during period 1 with technician services, and 7.7 min during period 2 with paramedic services. Ventricular fibrillation caused cardiac arrest in nearly all patients who survived; it occurred in 91 of the 160 (57%) patients during period 1 whose rhythms were determined and in 192 of the 343 (56%) patients during period 2. The decreased time from collapse to delivery of advanced emergency care accounted for the improved survival with paramedic services.