An ICD is a tiny, lightweight, electrical device that is placed inside your body. It keeps track of your heartbeat, and when necessary, it gives a small, low-voltage electrical pulse or shock to your heart, which forces it to beat or corrects an abnormal rhythm.
The ICD device consists of two parts: First, the battery unit, which is a small metal case that contains the power source, or pulse generator. This regulates how often signals are sent to the heart. The second part is the lead, which consists of one or two wires that carry electrical messages back and forth between the heart and the device.
These wires extend from the pulse generator and connect to the inside of your heart. ICDs control serious abnormal heartbeats. They also store information about your heart that the doctor can study or evaluate. Some patients say that an ICD is like having an emergency room right in your chest.