The Heartstart Scotland project for out-of-hospital defibrillation covers the whole of Scotland, a population of approximately 5,102,400 (14.9% > 65 years, 48.3% male). All 395 ambulances in Scotland have been equipped with an automated external defibrillator and crews are trained in basic cardiopulmonary resuscitation and defibrillator use (EMT-D). Between 1 May 1990 and 30 April 1991 a total of 1700 cardiac arrests was reported by the ambulance service. Of the 1676 arrests which we could trace, 63% were witnessed. A total of 1383 (83%) of all patients were declared dead on arrival at hospital or in the emergency department, 119 (7%) died in hospital and 174 (10%) were discharged alive. Of the 174 survivors, 87% were conscious and normal at discharge, 9% had moderate residual disability and 2% severe disability. Survival of patients discharged alive from hospital was 85% at 1 year. Defibrillation was undertaken in 71% of the reported cardiac arrests. Survival of bystander witnessed arrests was increased from 7 to 15% with bystander CPR (P < 0.005). If the cardiac arrest was witnessed by the ambulance crew and required defibrillation, survival to discharge was 39%. Of bystander witnessed arrests reached while still in VF (n = 643), 11% were discharged alive. Patients who were defibrillated within 4 min of arrest had a 43% survival rate to hospital discharge.