Sudden out-of-hospital cardiac arrest (OOH-CA) remains a significant cause of death, in spite of recent declines in overall mortality from cardiovascular disease. Several studies document sub optimal quality of manual chest compressions and this may influence outcome. However, studies comparing manual and mechanical chest compressions have resulted in conflicted results. The investigators think this may be based on methodology and design issues of the trials as much as not focusing on training and experience in operating a mechanical device clinically. Therefore the investigators will focus on these issues and implement three phases in the study (In field training, Run In phase, and Study phase). The investigators will also focus on early use of mechanical CPR after arrival at patient side and randomization at arrival. In order to achieve this the investigators will follow the Norwegian CPR Guidelines with 3 min CPR before defibrillation and the 3 min algorithm. Quality of CPR will be monitored.