A defibrillator is used to restore a normal heart rhythm by delivering an electrical shock to the heart when the heartbeat is dangerously fast due to ventricular tachycardia or ventricular fibrillation. Either of these conditions can be life-threatening, possibly causing the heart to abruptly cease pumping blood to the body (cardiac arrest), leading to sudden cardiac death.

At one point, defibrillators were used only by physicians in a hospital. However, recent technological advances have allowed people with minimal medical 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 (PADs) within moments of collapse significantly raises the survival rate from cardiac arrest and increases the likelihood of a meaningful recovery. Based  on these studies, the American Heart Association has endorsed the use of PADs. 

For patients suffering from chronic arrhythmias involving ventricular tachycardia or ventricular fibrillation, or certain patients at high risk of suffering from one of these conditions, there is a type of defibrillator that can be surgically implanted in a patient’s chest. This implantable cardioverter defibrillator (ICD) monitors for and, if necessary, corrects an abnormally fast or “quivering” heartbeat at the first sign of a problem.