An artificial heart that may extend the lives of dying terminal patients for several months has been approved by the Food and Drug Administration. The device is reserved for use by patients who are ineligible for a heart transplant and have less than a month to live.

The device, manufactured by Abiomed, Inc., was approved on Tuesday by the US Food and Drug Administration under the Humanitarian Use Device (HUD) provisions of the Food, Drug and Cosmetic Act.

The provisions were designed to encourage development of innovative medical devices to treat rare conditions affecting fewer than 4,000 people a year in the US. They allow medical devices to be approved for market if they demonstrate safety and probable benefit.

Only about 25 to 50 heart failure patients per year are expected to meet the eligibility requirements for the artificial heart, according to the FDA.

In a clinical trial involving 14 men, the AbioCor Implantable Replacement Heart extended survival for an average of four and a half months. All of the patients eventually died, but one man lived for 17 months with the device and another survived for 10 months.

Half the study participants died from strokes, and 50 incidents of severe bleeding were reported. Two patients did not survive the implantation surgery, and two others died within two months.

The two-pound titanium and plastic heart can only be implanted in people who are at least 6 feet tall and weigh at least 170 pounds, eliminating most female patients from consideration. It takes over the pumping function of the diseased heart, which is removed during the implantation procedure.

A power transfer coil powers the system across the skin and recharges the internal battery. In addition, a controller and an internal battery are implanted in the patient's abdomen.

The controller monitors the mechanical heart's pumping rate and other functions. The internal battery allows the patient to be free from external connections for as long as an hour.

Two external batteries let the patient move around freely for up to two hours. While the batteries are recharging, the system can be plugged into an electrical outlet.

The device is expected to cost around $250,000. Dr. Daniel Schultz, director of the FDA's Center for Device Evaluation and Research, said it is hoped that use of the device will lead to technological improvements as well as cost reductions.

The ultimate goal is to develop a mechanical heart that can be used instead of a heart transplant. In the meantime, many dying patients are expected to welcome the chance to have additional time with family and friends, despite the current limitations of the technology and the expense.

"We hope today's approval will encourage the continued development of potentially life-saving technologies for critically ill patients," Schultz said.

Abiomed is working on a new artificial heart that could be ready for use by 2008, Chairman and Chief Executive Michael Minogue told reporters. The newer device is about two-thirds the size of the current AbioCor, and officials hope it will extend patients' lives by five years.