Steady improvements have been made through five systems for operating an artificial heart with a Stirling engine that will be heated by a radioisotope or by an electric heater which receives power from a transcutaneous transformer. A thermal storage reservoir assists in supplying peak power demands. The engine regenerator, a primary component, was substantially improved by changing from a porous to a hollow regenerator. Engine efficiency was doubled. The current engine, using a hot flexural support at the engine, a bellows-sealed lower support, a drive piston, and a flywheel for continuity of regenerator motion, has been quite successful. Potential reductions in size and isotope requirement are discussed. The computed dose rate for the system is also given. Development is continuing toward a reliable realistically sized artificial heart with reasonable power demands.