Even for paramedics and emergency physicians, the resuscitation of patients with cardiac arrest remains a challenge. Previous studies have shown that the cardiac output varies widely even among professional helpers. This is especially due to some very different mean frequencies of cardiac compression wich vary from 60 to 160/min for paramedics. Aim of this study is to investigate whether the use of feedback-devices during cardiac-pulmonary resuscitation (CPR) can lead to an improvement of the cardiac output and may improve survival.