What is an implantable cardioverter defibrillator (ICD)?

An implantable cardioverter defibrillator (ICD) is a small battery-powered device, similar to a pacemaker, that is implanted under the skin, often in the shoulder area, just under the collarbone. Thin wires connect the ICD to the heart. An ICD senses the rate of the heartbeat. When the heart rate exceeds a rate programmed into the device, the ICD delivers a small, electrical shock to the heart to slow the heart rate. Many newer ICDs can also function as a pacemaker by delivering an electrical signal to regulate a heart rate that is too slow or pace out of a rapid rhythm.