Earlier this month, the first fully implantable artificial heart was approved by the Food and Drug Administration. It brings hope to patients who are near death from heart failure; yet some major problems remain with it--namely, its large size and relatively short lifespan.

A new concept for an artificial heart could solve some of those issues. But its innovative pulse-free architecture might also raise problems of its own.

Artificial hearts work by pumping deoxygenated blood from the body to the lungs. The device then pumps oxygenated blood through the body. The newly approved device, called AbioCor, made by Massachusetts-based Abiomed, uses an implanted hydraulic pumping system to simulate a natural heart beat. But an alternative design, conceived by O.H. "Bud" Frazier, a prominent heart surgeon and pioneer in the development of cardiac devices at the Texas Heart Institute in Houston, pumps blood through the body continuously, rather than with the periodic beat of the normal heart.

Pumps that work on this principle, known as continuous flow pumps, are already in clinical use as part of "ventricular assist devices," which are implanted into patients with some remaining heart function to help circulate blood through the body. (Artificial hearts replace the heart entirely.)

"Continuous flow pumps are like little turbo machines," says Tim Baldwin, program director of the advanced technologies and surgery branch of the National Heart, Lung and Blood Institute in Bethesda MD. "They are more durable and allow you to make smaller devices."

With Frazier's continuous flow design for an entirely artificial heart, a severely damaged heart is removed and replaced with two rotor-based pumps that continually cycle blood through the body, completely taking over the function of the heart.

In preliminary experiments conducted over the last two years, Frazier and his team have implanted pairs of commercially available ventricular-assist devices into calves that had their hearts removed. The researchers say the devices were able to pump blood and respond to the animals' needs based on their activities. "You put this in cattle and they stand up and moo and eat and wonder why everyone is looking at them so weird," says William Cohn, a collaborator on the research and director of minimally invasive surgical technology at the Texas Heart Institute. "You see a cow wagging his tail and you say, wow, this is the future of the artificial heart."