Implantable cardioverter-defibrillators (ICD) is a device implantable inside the body and is able to perform cardioversion and pacing of the heart.The device is capable of correcting many life-threatening cardiac arrhythmias. Perhaps, many devices can be programmed which helps to detect abnormal heart rhythms and delivers therapy via programmable antitachycardia pacing in order to low energy and high energy shocks. The actual process of implantation of an ICD system is very similar to the implantation of the pacemaker and is composed of an ICD generator and many wires. The first and most important component has a computer chip or circuitry with a RAM memory and the second part is an electrode wire and is similar to the pacemakers which are connected to the generator and passed through the vein to the right chambers of the heart. A battery which is powered is implanted into a pouch under the skin of the abdomen and just below the collarbone. The actual generator is about the size of a hand watch and wires lead from the pulse generator to the various positions of inside the hearth and can be installed through the blood vessels which eliminates the need for open-chest surgery. These new devices are good in detecting abnormal heart rhythm and also offer a host of many sophisticated functions.