Pacemakers. Pacemakers are used to sense the heartbeat and if no heartbeat is detected, an electrical impulse to stimulate the heart is provided. Therefore, components of a pacemaker are 1. Sensor 2. Power supply to deliver an electrical impulse 3. Leads that connect the body of pacemaker to the heart. Current day pacemakers are very small, almost size of a large coin. Circuitry is inside a titanium can.
Metal. Metal and microchips. Pacemakers are actually little computers and are made of material that are similar to the device you used to type your question inside a metal can.