An Implantable Cardioverter Defibrillator (ICD) is a battery-powered device placed under your skin, beneath the collarbone, that is connected to your heart by one or more wires (leads) and keeps track of your heartbeat. The ICD detects dangerous heart rhythms (arrhythmias) then sends electrical signals that ‘shock’ your heart out of the dangerous rhythms and allow normal rhythms to resume.