Implantable defibrillators represent the most significant innovation to thwart sudden cardiac death caused by ventricular arrhythmias. Devices have also been designed for the treatment of atrial fibrillation. ICDs are generally implanted in subjects who have withstood more than one incident of ventricular tachycardia or fibrillation. They are also applicable in subjects whose clinical synopsis indicates highly probable, up-and-coming persistent ventricular tachycardia or fibrillation. Chosen highly suggestive subjects with atrial fibrillation too can benefit from ICDs. In contrast to pacemakers, ICDs are endowed with capability of dispensing electrical shocks of high energy to the heart. These shocks are imparted to set right serious, life-threatening, rapid, and sustained arrhythmias. Ventricular fibrillation and ventricular tachycardia are such arrhythmias. Atrial fibrillation too has devastating effects. Such abnormalities are unmanageable by pacing with electrical pulses of low energies and are often irredeemable if not bothered about. The battery chemistry of ICDs uses silver vanadium pentoxide. Large and bulky capacitors are necessary to change the 3–6 V battery output into the 750 V shock required to defibrillate a heart.