Dr. Dharmabalan writes in IMA CGP WhatsApp Journal:

An implantable cardioverter defibrillator (ICD) is a tiny computer, plus a battery, contained in a small titanium metal case that is about the size of a pocket watch. It weighs approximately 3 ounces.

The ICD is implanted under your skin, typically on the left or right side of your chest, just below the collarbone. In addition to the device itself, leads (tiny insulated wires) are implanted for two purposes: to carry information signals from your heart to the heart device, and when necessary, to carry electrical impulses to your heart.

The third part of your implantable device system is a programmer, an external computer located in your doctor’s office or clinic that is used to program the heart device and retrieve information from your device that will assist your doctor in your treatment.

ICDs feature a defibrillator to treat fast heartbeat and pacemaker therapy to detect and correct slow or irregular heart rhythms. ICDs are completely automatic. They constantly check your heart and device functions, and adjust as needed.