The shy former assistant manager of a grocery store in a small northern Arizona town today became the first person to have his heart replaced with an authorized mechanical model and then a human transplant.

The patient, Michael Drummond, 25, who had been dying of cardiomyopathy caused by a viral infection he contracted about six months ago, was listed in critical but stable condition after the transplant operation today.

The four-hour, 45-minute surgery was performed early this morning here at University Medical Center by Dr. Jack G. Copeland. Drummond received the heart of Tarro Griffin, 19, of Lindale, Tex., who was killed in a traffic accident.

In March, Copeland and Dr. Cecil Vaughn, a Phoenix heart surgeon, implanted a little-tested artificial heart crafted by a Phoenix dental surgeon into a 33-year-old former auto mechanic, Thomas Creighton, who was rejecting a transplant. Creighton died after an effort to replace that artificial heart with a second human transplant.

That artificial heart, dubbed the Phoenix heart, was not approved for use in humans by the Food and Drug Administration.

Although FDA regulations approving experimental implantation of the Jarvik-7 mechanical heart at University Medical Center specified that any recipient must be a viable candidate for a human-heart transplant, Copeland said today that because of Drummond's failing health, "I seriously question whether we would have considered him a reasonable candidate for transplantation at the time the Jarvik was implanted."

Drummond had been hospitalized in Phoenix suffering from congestive heart failure in April and was admitted to the medical center on Aug. 26 for evaluation as a possible heart-transplantation candidate. His condition deteriorated. Tests indicated that he was suffering from pulmonary edema and acidosis -- a potentially fatal diagnosis -- and he became a transplant candidate.

On Aug. 29, Drummond began to have severe ventricular arrhythmia. His blood pressure dropped, and the decision was made to implant the Jarvik-7 heart.

Both Drummond and his parents were initially opposed to participating in the experimental Jarvik-7 program, but changed their minds after deciding it was worth the risk to be able to buy even a few more hours of life.

After the Jarvik-7 was implanted Aug. 29, Copeland announced his intention to leave the temporary device in place for several days or longer, if necessary, to try to permit Drummond to recover from that surgery before beginning a second major surgery, to insert a transplant.

After Drummond suffered a series of small strokes Wednesday morning, Copeland changed his mind. A call went out nationwide for a suitable heart for Drummond.

Throughout today's surgery, Drummond's neurological status was monitored to check that he was not suffering further strokes as the Jarvik was being removed and the donor heart stitched into place.

After it was removed from Drummond's chest, the Jarvik-7 was prepared for shipment to the manufacturer, Symbion Inc., in Salt Lake City, where it will be examined for flaws or anything else that could have affected Drummond.

Drummond's recuperation period is expected to be longer than the three weeks that most heart-transplant patients remain hospitalized here, because he was so weakened by the progression of his heart disease.

Vaughn, who assisted Copeland in the Drummond and Creighton operations, said Drummond's surgery was "much more organized. . . . We learned a lot of things in an organized way that we had to learn by flying by the seat of our pants before."