The pacemaker on the X-ray Nope, it is not placed inside the heart, as many people think. A pacemaker is this strange "thing" near your collarbone that has "wires" coming from it. And these wires go to the heart — they transmit an impulse to the myocardium (the muscular membrane of the heart), which causes the organ to contract. On an x-ray, the heart is a bright area in the center (in medicine, this is called the opposite — darkening).