An implantable defibrillator is a device, which is used to monitor heart rate. It uses batteries to send electric signals to a heart that's beating too slow, similar to a pacemaker. It can also deliver an electric shock to help restore a normal heartbeat to a heart that's beating chaotically and much too fast. Cardiac defibrillation is a way to return an abnormally fast or disorganized heartbeat to normal with an electric shock. The device is inserted under the skin in the chest or abdomen.  The procedure is similar to that of a pacemaker insertion. One wire is connected to the heart and another is connected to the defibrillator unit. The defibrillator unit monitors the heart rhythm, sends an electrical shock and keeps a record of the events. If the heart is beating normally, the ICD is inactive. When an abnormal, fast heart rate, known as a tachycardia, is detected, the ICD will send electric shock signals to the heart. The electric shock converts the abnormal rhythm to a normal rhythm. The low energy electric shocks delivered by the ICD do not harm the patient or anyone in physical contact with the patient.  The patient may feel the symptoms of the tachycardia as it begins.