The purpose of CPR is for the rescuer to do the job of the heart by pumping on the victims chest. By pumping on the victims chest the rescuer helps circulate oxygenated blood throughout the body helping keep body cells alive. Use automated external defibrillator (AED) if available in a CPR situation if available.
Defibrillators administer a controlled electric shock that allow restoration of a normal rhythm. Devices such as AED will tell you when defibrillation is needed. Early recognition, effective CPR and Defibrillation increase the chance of return of spontaneous circulation in the heart. This means that the heart has began beating again.