Defibrillators which monitor quality of CPR via changes in thoracic impedance (for ventilation) and movement of the sternum employing an accelerometer (for chest compressions) will be employed in ambulances in Akershus county (Norway), Stockholm (Sweden) and London (UK). During phase 1 quality of CPR will be monitored without feedback from the defibrillator. During phase 2 the ambulance personnel will receive feedback via the defibrillator. During phase 3 the ambulance personnel will be retrained with particular attention to the quality problems that became apparent in phase 3.