The invention and development of the heart pacemaker illustrates the merging of medicine and engineering. The device is a result of the collective efforts and collaboration of people and organizations from both engineering and medicine, and both public and private institutions. The pacemaker was the first electronic device ever surgically implanted inside a human.

First developed in the 1960s, pacemaker typically refers to a small, battery-powered device that helps the heart beat in a regular rhythm. Small electrical charges travel to one or multiple electrodes placed next to the heart muscle.

Originally pacemakers sent one steady beat to the heart through a single electrode. Today's pacemakers can sense when a heart needs help and delivers just the right amount and duration of impulse---sometimes through multiple electrodes---that maintain steady heart rate, even during physical activity. While most pacemakers today are permanent implants, some are used as temporary therapy for recovering heart patients. Most pacemakers have a sensing device that turns itself off when the heartbeat is above a certain level. It turns back on when the heartbeat is too slow.

Since the early 1800s, scientists have known that electricity could stimulate an inactive heart to beat. In 1950, electrical engineer John Hopps built the first pacemaker while conducting hypothermia research at the National Research Council. But Hopps's device was too large to be implanted in humans, it relied on external electrodes, and it had to be plugged into a wall outlet. External electric shocks were frequently too traumatic for patients with heart block, where the heart's own electrical impulses dwindle, and the AC-operated pacemaker could fail during a power blackout.

In the mid-1950s, open-heart surgeons in Minneapolis set out to develop a better system, and teamed with a local electric medical equipment company, Medtronic, run by engineer Earl Bakken. By 1957, the research team discovered that by combining a pulse generator with a wire electrode attached directly to the hearts of dogs, heart rates could be controlled. Bakken developed a new pacemaker not much larger than a paperback book that was powered by mercury batteries, provided a 9-volt DC pulse, and could easily and comfortably be worn by young patients.

When Bakken's pacemaker was tested in the laboratory on a pediatric heart block patient, its effect was instantaneous. The pacemaker immediately restored the child's heartbeat to near normal. Within days, the child's heart resumed a normal rhythm on its own and the pacemaker was removed.

In most cases, the external pacemaker was used by patients recovering from open heart surgery. Several physicians, however, recognized the value of the device in treating patients suffering from chronic heart block. Yet, long-term application presented several problems: an external pacemaker worn 24 hours a day was inconvenient for the patient, the wires could become dislodged from the heart, and most important, the passage of wires through the skin to the heart introduced the possibility of infection.

The first successful attempts at designing a totally implantable pacemaker were reported by Drs. William Chardack and Andrew Gage at the Veterans Administration Hospital in Buffalo, New York, and Wilson Greatbatch, an electrical engineer from upstate New York.

Greatbatch was building an oscillator to record heart sounds. When he accidentally installed a resistor with the wrong resistance, the unit began to give off a steady electrical pulse. Greatbatch realized that the small device could be used to regulate the human heart. After two years of refinements, he had handcrafted the world's first successful implantable pacemaker. Until that time, the apparatus used to regulate heartbeat was the size of a television set, and painful to use.

Greatbatch and his team worked for two more years to develop the device. He later went one step further, inventing a corrosion-free lithium battery to power the pacemaker. The goup's work was recognized by Medtronic, which in 1960 signed a contract with Chardack and Greatbatch to produce an implantable pulse generator. These pacemakers and batteries have improved and saved the lives of millions of persons worldwide.

After development of the implantable pacemaker in 1960, significant advancements in all areas of pacing occurred rapidly. Other advancements included transvenous leads, better methods of fastening and holding the electrodes to the heart, more efficient electrodes and power sources, and more intelligent pacing that can react to the patient's varied needs.

Pacemakers today are implanted using local anesthetic, under a flap of skin in the chest or abdomen. One or more electrodes are threaded through a vein from the device to the right side of the heart. The device today may be as small as one inch (2.5 cm) in diameter and weigh as little as 0.5 oz. (14 gm). Modern versions can monitor the heart and activate themselves only when necessary; they are also less sensitive to outside sources of electromagnetic radiation than earlier versions. Most pacemakers run on lithium batteries, which need to be replaced about every 10 years.