When the natural heart is partly damaged or diseased, patients might keep it and have a mechanical aid implanted to bolster blood flow. Such pumps — especially those that aid the left side of the heart — are in wide use both as a bridge to a transplant and for lifetime therapy.

A totally artificial heart for extended use would be of great value, but it’s far too early to know if the Carmat heart, as yet untried in humans, will be that device. “The whole history of mechanical devices is that people thought they had devices where blood wouldn’t clot. But they didn’t,” Dr. Stevenson said.

Dr. Jansen said that the cost of the Carmat heart would be about $200,000 and that he did not expect it to be brought to market in Europe before the end of 2014. Once the company gains momentum with its European clinical studies, he said, it plans to start working through the regulatory process in the United States.

The Carmat heart has two chambers, each divided by a membrane. That membrane has cow tissue on one side — the side that is in contact with blood — and polyurethane on the other side, which touches the miniaturized pumping system of motors and hydraulic fluids that changes the membrane’s shape. (The motion of the membrane pushes the blood out to the body.) The embedded electronics and software adjust the rate of blood flow. Patients can wear the batteries under the arm in a holster, or in a belt, among other options.

Cow tissue is also used for the heart’s artificial valves, which were created by Dr. Alain Carpentier, a cardiac surgeon and a pioneer of heart valve repair who is also a co-founder of Carmat and its scientific director. Such valves have been used in heart-valve replacement surgery for decades. The cow tissue is chemically treated so that it is sterile and biologically inert.

The heart’s design and development relied heavily on aerospace testing strategies by EADS, the European Aeronautic Defense and Space Company, one of Carmat’s backers, Dr. Jansen said. Even so, duplicating the durability of a human heart will not be easy, said Dr. Robert Kormos, director of the artificial heart program at the University of Pittsburgh Medical Center and co-director of its heart transplant program.