Introduction: early defibrillation in patients in cardiac arrest (CA) and with Ventricular Fibrillation or Ventricular Tachycardia (VF - VT) is the treatment of choice.Aim: to evaluate the benefit, in terms of survival, of delegating electrical defibrillation of VF or VT by the 100 ambulancemen who arrive next to the victim within 5-10 min. in an urban setting before arrival of the S.M.U.R. (Service Mobile d'Urgence et de Reanimation).Methods: extrahospital cardiac arrest in Brussels; 400 100 ambulancemen trained at using Semi Automatic External Defibrillation (SAED); 50 % of the 100 ambulances equipped with a SAED; guidelines of the European Resuscitation Council respected.Results:Conclusion: delegation of SAED in extrahospital cardiac arrest to 100 ambulancemen increases significantly the survival at the exit of hospital in all patients and particularly in patients with ventricular fibrillation or ventricular tachycardia.