An implantable cardioverter-defibrillator (ICD) is a small device placed under the skin of the chest to monitor and regulate abnormal heart rhythms. It consists of a generator that delivers electrical shocks or pacing pulses to restore normal heart rhythm when necessary. During the implantation procedure, a small incision is made to insert the device, usually near the collarbone, and leads are threaded through veins into the heart. The ICD continuously monitors the heart's electrical activity, detecting irregularities and delivering appropriate therapy, such as electrical shocks to stop life-threatening arrhythmias, ensuring the patient's heart functions properly and reducing the risk of sudden cardiac death.