Implantable cardioverter-defibrillator (ICD) is a small battery-powered electrical impulse generator that is implanted in patients who are at risk of sudden cardiac death due to ventricular fibrillation and ventricular tachycardia. It detects cardiac arrhythmia and correct it by delivering a jolt of electricity. Ability to revert ventricular fibrillation. Can include both atrial and ventricular arrhythmias. Can perform biventricular pacing for congestive heart failure or bradycardia.