Implantable Cardiac Defibrillators (ICDs) are for people who have had an abnormal, fast heart rate that caused them to faint or caused their heart to stop pumping properly. Sometimes medicines can be used to control these fast heart rates. When medicines do not work, doctors can implant an ICD. An ICD is used in patients at risk for three reaons. Ventricular tachycardia, when the lower chambers of the heart independently beat faster than 100 beats per minute; ventricular fibrillation, when the muscle fibers of the lower chambers of the heart contract in a fast, uncoordinated manner or for sudden cardiac death caused by arrhythmias.