During a period of 3 years three different types of emergency medical service (EMS) systems were evaluated in a city with about 238,000 inhabitants/population density of 570/km2. Included were 393 out-of-hospital cardiac arrest patients in whom prehospital cardiopulmonary resuscitation was provided by personnel on basic, intermediate, or advanced care training. When ordinary ambulances (basic EMS) were used, 8 (5%) patients were discharged alive. When ambulances with specially trained paramedics (intermediate EMS) were used, 2 (1%) patients were discharged. Finally medically staffed ambulances with doctors collaborating (advanced EMS) were used, and 11 (13%) patients were discharged. The intermediate EMS system was used in another area with 45,000 inhabitants/population density of 340/km2, and in this area 20 (18%) patients were discharged. Among the survivors a psychological assessment in form of a test for dementia was assessed in long-term survivors (n = 30) together with 28 patients surviving acute myocardial infarction and 11 control persons. The results of the investigation demonstrate that the more intensive the prehospital treatment of out-of-hospital cardiac arrest, the more patients survive and the more patients survive with good cerebral function. However, the ambulances with specially trained paramedics were only effective in the area with 340 inhabitants/km2.