An implantable cardioverter-defibrillator (ICD) — a pager-sized device — is placed in your chest to reduce your risk of dying if the lower chambers of your heart (ventricles) go into a dangerous rhythm and stop beating effectively (cardiac arrest).

You might need an ICD if you have a dangerously fast heartbeat (ventricular tachycardia) or a chaotic heartbeat that keeps your heart from supplying enough blood to the rest of your body (ventricular fibrillation).

ICDs detect and stop abnormal heartbeats (arrhythmias). The device continuously monitors your heartbeat and delivers electrical pulses to restore a normal heart rhythm when necessary.

An ICD differs from a pacemaker — another implantable device used to help control abnormal heart rhythms.