For many of the nation’s five million people suffering from congestive heart failure, treatment options are grim. When weak heart muscles stop pumping blood efficiently, many patients require cumbersome cardiac-assist devices driven by heavy external battery packs. Some even plug into an outlet, ruling out treks beyond the hospital.

Now a wireless alternative is on the way. Researchers at Allegheny General Hospital in Pittsburgh have invented a completely self-contained hydraulic pump that requires no external power source. Called a muscle energy converter, or MEC, the device turns skeletal muscles into living batteries, harnessing their vast stores of mechanical energy to power an implant.

Once situated in the chest, the nine-ounce titanium device is fastened to the rib cage. An artificial tendon connects an actuator arm on the device to a back muscle, which is stimulated by implanted electrodes. When the muscle contracts, it moves the actuator arm, which then rotates a cam and generates hydraulic power for the implant.

The MEC by itself works well in canines. Next up: attaching it to a heart implant. Expect muscle batteries for humans by 2010.