While many people might be most familiar with the external defibrillators seen on TV, in emergency rooms or at sporting events, there are related devices that, although less obvious in their use, serve the same purpose of restoring prissy heart rhythms and thus averting viable death by cardiac arrest or heart attack. They are called implantable cardioverter defibrillators but are often referred to as pacemakers. An implantable cardioverter defibrillator is a device designed for individuals with definite forms of heart disease of defects that put them at recurring risk of sustained ventricular fibrillation, or cardiac arrest. The device is established either within the chest itself, or more commonly today within the blood vessels thus eliminating the need for dangerous open chest surgery.