Is 3 minutes of CPR before defibrillation, better than immediate defibrillation, for patients who are found to be in cardiac arrests by paramedics?

This study is testing whether giving 3 minutes of CPR (cardiopulmonary resuscitation) before using a defibrillator (electric shock to the heart) is better than delivering the shock immediately for people found to be in cardiac arrest out-of-hospital. Some research suggests that preparing the heart with a brief period of CPR first may improve the chance of survival. Paramedics will apply one of these two approaches and the study will measure how many patients survive to hospital. You may be eligible if: - You are 18 years of age or older - You are in cardiac arrest out of hospital - The first paramedic on scene finds you in ventricular fibrillation (a dangerous abnormal heart rhythm) You may NOT be eligible if: - Your cardiac arrest was caused by trauma (injury) - Your cardiac arrest was witnessed before paramedics arrived - A medical professional had already started treatment (intubation or drugs) before paramedics arrived (note: bystander CPR is not an exclusion) - You have a 'do not resuscitate' order or similar documentation Talk to your doctor about whether this trial might be right for you.