How Does a Pacemaker Work?

A cardiac pacemaker is a small device implanted under the skin near the collarbone, with leads threaded into the heart chambers. When its sensors detect that the heart rate has dropped below a programmed threshold — typically around 60 beats per minute — it delivers tiny electrical pulses (1–5 volts) to stimulate contraction. Modern dual-chamber pacemakers coordinate both atria and ventricles for natural rhythm. Over 1 million pacemakers are implanted worldwide each year, and lithium-iodide batteries now last 7–15 years before replacement is needed.