A pacemaker is a tiny, lightweight, electrical device that is placed inside your body usually in the chest near the shoulder. It keeps track of your heartbeat and when necessary it gives a small low-voltage electrical pulse to your heart, which forces it to beat. The pacemaker 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 pacemaker. These wires extend from the pulse generator and connect to the inside of your heart.
The device is much smaller than a deck of cards and weighs slightly more than an ounce.