A defibrillator is a device that attempts to restore a normal heart rhythm by delivering an electrical shock to the heart. A defibrillator is used when the heartbeat is dangerously fast due to ventricular tachycardia or ventricular fibrillation. Either of these conditions can be life-threatening because the heart may abruptly stop pumping blood to the body (cardiac arrest). Some defibrillators are external (e.g., defibrillator paddles in an emergency room), and some are surgically implanted in the patient’s chest (e.g., an implantable defibrillator cardioverter).

Recent advances in technology have allowed people with little training to use automatic external defibrillators (AEDs) in an emergency when medical professionals are not present. Studies have shown that use of public access defibrillators (PAD) within moments of collapse significantly raises the survival rate from cardiac arrest, with between 50 percent and 74 percent of victims surviving their collapse. Based on these studies, the American Heart Association has endorsed the use of PADs.