A Jarvik-7 artificial heart was implanted yesterday in a 25-year-old man, the youngest recipient of the mechanical pump, while doctors searched for a new human heart for him.

Michael Drummond of Phoenix, an assistant supermarket manager, was reported in critical but stable condition after the surgery at the University Medical Center.

He is the sixth man to receive the Jarvik-7 heart, and the first to do so at the University Medical Center. The hospital received approval from the Food and Drug Administration on Aug. 21 to implant the device.

Unlike the previous implants, Drummond's Jarvik-7 is not intended as a permanent replacement, Dr. Jack Copeland, who led the University of Arizona team that performed the operation, said.

Copeland said he expects Drummond to remain on the Jarvik-7 heart for one to two weeks until doctors can find a human donor heart.

"Mr. Drummond is doing fine . . . . The operation went well," Copeland said. "Right now I feel very good about what's going on. I have a lot of fears about what's going to happen."

Drummond had some fluid in his lungs that had existed before the operation, the surgeon said, adding that reducing the fluid was doctors' immediate goal.

Dr. Robert Jarvik, who invented the device and who arrived during the operation, said Drummond's chances were "a little bit better or perhaps a lot better" than previous artificial heart patients because the others generally had more damage to their other organs.