The Food and Drug Administration has approved experimental use in humans of a fully implantable, battery-powered artificial heart.

Abiomed Inc., the Danvers-based company that makes the 2-pound, fist-sized pump, said Tuesday the FDA approved use of the device in five patients, all of them too sick for heart transplants.

The grapefruit-sized artificial heart is inserted in the body along with a rechargeable battery that can work on its own for about 30 minutes. The battery can be recharged through the skin.

The patient can also wear an external battery pack that can last for several hours. The mechanical heart, called the AbioCor, is expected to enable patients to participate in normal activities, including light sports.

Earlier versions of an artificial heart, including the Jarvik-7, were powered outside the body. The latest device, which has been tested on calves, is designed as a permanent replacement to a heart transplant.

The AbioCor will sell initially for $75,000 to $100,000, analysts projected, making it comparable to the cost of open heart surgery, but less than the cost of heart transplant surgery.

An estimated 100,000 Americans suffer from end-stage heart failure each year, but only about 2,000 human hearts are available for transplants.

"The medical system desperately needs something to fill in that very big gap," said Phillip E. Nalbone, an industry analyst with Salomon Smith Barney in San Diego.

Tests on the device were to be conducted on patients at Hahnemann University Hospital in Philadelphia; Jewish Heart Lung Hospital in Louisville, Ky.; the Texas Heart Institute in Houston; and Massachusetts General Hospital and Brigham and Women's Hospital in Boston.

The implantation procedure would have to be reviewed and approved by the hospital's institutional review board, which goes over experimental procedures to make sure they're safe.

The AbioCor is expected to be much more advanced than the Jarvik-7, which kept several people, including retired Seattle dentist Barney Clark, alive for several days in the early 1980s.

The Jarvik-7 was considered a failure because Clark suffered strokes and severe depression while he was tethered to a power source the size of a washing machine. That device was eventually recalled.