Cardiopulmonary resuscitation: A life-saving emergency procedure that involves breathing for the victim and applying external chest compression to make the heart pump. Abbreviated CPR. In the early stages of a heart attack, death can often be avoided if a bystander starts CPR within 5 minutes of the onset of ventricular fibrillation. When paramedics arrive, medications and/or electrical shock (cardioversion) to the heart can be administered to convert ventricular fibrillation to a normal heart rhythm. Prompt CPR and rapid paramedic response can improve the chances of survival from a heart attack.