A pacemaker is a small electronic device that doctors surgically place inside someone's chest to help their heart beat with a steady, healthy rhythm. Your heart is a muscle that pumps blood throughout your body, and it needs to beat at just the right speed: not too fast, not too slow, and not skipping beats. When someone's heart doesn't keep this rhythm naturally, a pacemaker can take over that job.

The device is about the size of a large coin and contains a battery and tiny computer. It connects to the heart through thin wires and sends gentle electrical signals that tell the heart when to beat. The pacemaker constantly monitors the heart and only steps in when needed, like a backup system that springs into action.

In competitive running, a pacemaker (also called a pacer or pacesetter) is a runner whose job is to set a steady speed for other runners to follow. In major marathons, elite runners often rely on pacemakers to maintain an even tempo through the early miles of the race. Just as that runner sets the pace for others, the medical device sets the pace for your heartbeat, keeping everything running smoothly and steadily.