A prototype pacemaker tested in pigs gets one sixth of its power from the beats of the organ it regulates.

The generator, developed at Southampton University Hospital in the UK, consists of two small liquid-filled balloons placed at separate locations within the heart and connected by a silicone tube containing a moveable magnet.

As the heart beats, it squeezes each balloon in turn, pushing liquid through the tube and forcing the magnet to move back and forth past a coil embedded in the tube. This generates electricity that can be used to recharge the battery.