pacemaker

Think of a reliable metronome that taps out a beat whenever the band slows down or skips. A pacemaker is a small implanted device that watches the heart and delivers tiny electrical pulses to keep it beating at a safe rate when its own natural pacing falters.

The device has two parts: a small battery-and-computer unit (the generator), usually placed under the skin below the collarbone, and one or more thin insulated wires (leads) threaded through a vein into the heart. The pacemaker constantly senses the heart’s own electrical activity and steps in only when needed — for example, if the heart beats too slowly or a beat is dropped — by sending a pulse that prompts the muscle to contract.

Pacemakers chiefly treat slow heart rhythms (bradycardia) and conduction blocks where the heart’s wiring fails to carry signals properly, such as complete heart block or sick sinus syndrome. They do not treat blocked arteries or heart failure pump weakness directly, though a specialized type used in heart failure (resynchronization therapy) coordinates the two ventricles. Some modern pacemakers are tiny and leadless, sitting entirely inside the heart.