Electronic pacemakers time the heartbeats of more than three million people in the U.S. For these patients, surgery is a regular occurrence. A pacemaker's batteries must be swapped out every five to eight years, and the electric leads that connect the device to the heart can wear out, too.

In an effort to eliminate the batteries and leads altogether, biomedical engineers at the University of Bern in Switzerland have built a heartbeat-powered pacemaker, assembled from self-winding clockwork technology that is more than two centuries old.

Automatic wristwatches, invented in 1777, contain a weighted rotor that turns when a wearer's wrist moves. The rotor winds up a spring, and when the fully coiled spring unwinds, it turns the watch's gears. In modern versions, the gears drive a tiny current-producing generator.

Like the jostling of a wrist, a beating heart can also wind a spring, the Swiss team found. The researchers stripped an automatic wristwatch of its time-indicating parts, enclosed the winding mechanism in a three-centimeter-wide case and sutured it to a live pig's heart. The prototype produced 50 microwatts of power; pacemakers need about 10.

The device currently has a “messy setup,” says Adrian Zurbuchen, who presented details about it at the European Society of Cardiology Congress late last summer. Wires connect the watch parts to a box containing electronics and a pacemaker. The goal is to have everything in one device. It will not be ready for prime time soon, predicts Spencer Rosero, who is director of the pacemaker clinic at the University of Rochester Medical Center and was not involved in the project. He says if tests are successful, medicine will most likely first see a pacemaker with both a battery and energy-harvesting components.