Often times implanted medical devices are limited to their energy supply. Once that runs out, doctors are required to surgically explant a working device just to replace the battery. Mr. Zurbuchen, a PhD candidate at University of Bern, Switzerland, created a pacemaker that solely runs on energy generated by the motion of the heart. 
His prototype and original inspiration came from the commonplace wristwatch. The pacemaker works in roughly three steps. First, when the external environment accelerates or creates motion (i.e. the heart), the clockwork within the pacemaker begins rotating. This rotation winds up a mechanical spring in which it later unwinds and spins an electrical generator. Second, the energy is transferred through an electronic circuit into a small buffered capacity. Lastly, the stored energy is used to apply a small stimulus to the heart when needed.
This device has already been successfully tested on domesticated pigs. However, there is still more work to be done on this device. The parts in each step are still separate and the researchers are working on a way to integrate each step into one implantable device.
From the news release:
Mr. Zurbuchen said: “We have shown that it is possible to pace the heart using the power of its own motion. The next step in our prototype is to integrate both the electronic circuit for energy storage and the custom-made pacemaker directly into the harvesting device. This will eliminate the need for leads.”
Press release from the European Society of Cardiology: Batteryless Cardiac Pacemaker…