The factors influencing the decision to initiate resuscitation in prehospital cardiac arrest patients encountered in bradyasystole due to presumed heart disease were studied. For this purpose, the characteristics and circumstances of arrest of the patients encountered in asystole and electromechanical dissociation, seen by a physician-staffed prehospital emergency care unit in a tiered emergency medical system, were reviewed. During the study period, resuscitation was initiated in 83 bradyasytolic patients. The characteristics of these patients were compared with those of 72 patients in asystole or electromechanical dissociation declared dead on the scene without resuscitation. The presence of EMD was the most important factor influencing the decision to resuscitate (P less than 0.001), even if the arrest was unwitnessed, while the patient's age was of less importance. For the patients with a witnessed arrest, the delay before treatment was initiated also affected the decision. Successful resuscitation and survival of the patients was similar to earlier reports. The results provide guidelines in the decision making of initiation of resuscitation when developing our emergency care system into one with non-physicians as advanced life support providers.