The "Jarvik 7" artificial heart implanted Thursday for the first time is not an "invention but a replication" of the human heart that it replaces, University of Utah official Chase Peterson said today.

Named for designer Robert Jarvik, it is a two-chambered machine that replaces the heart's ventricles, the large, lower pumping chambers that send blood out to the lungs and body. Surgeons leave behind the smaller upper chambers, or atria, as an attachment for the mechanical device.

A model of simplicity, it operates much as the natural heart does. Blood from the body is brought through the veins to the right atrium and moves through an artificial valve into the man-made right ventricle. It leaves this chamber through the pulmonary artery, and goes to the lungs where it leaves behind carbon dioxide and takes up needed oxygen.

Then it comes back to the left upper chamber and repeats the process, moving into the artificial left ventricle and out to the body through the aorta.

While mechanically it is the same, the artificial heart and its outside power drive system have one major difference: It can be controlled. Doctors set the heart rate at a given level, as well as the percentage of heart beat devoted to the ejection of blood.

But, explained Dr. Kevin D. Murray, the mechanical heart can automatically make its own adjustments to changing situations. While the normal heart beats faster to pump more blood, devices inside the artificial heart react to the amount of blood returning to the heart from the body. At rest, less blood is needed, but with exercise the blood flow increases.

The artificial heart is slightly larger than the normal heart, but weighs about the same, 280 grams. It makes a low "click-click" sound inside the chest and the external power system makes a whirring noise.