The failing heart of a Swedish man with "an enormous will to live" was replaced Sunday with a Jarvik-7 artificial device in the first such operation outside the United States, doctors at Stockholm's Karolinska Hospital announced yesterday.

Dr. Bjarne Semb, a Norwegian surgeon who led a 12-member team in the lengthy operation, said at a news conference in Stockholm yesterday that the patient, identified only as a man in his fifties, was in "unexpectedly good shape" and was now "off the respirator, awake and talking."

"It was a successful operation, but it is too early to tell if he will make it," Semb told reporters. Hospital officials said that the patient, whose heart had been weakened by two massive heart attacks, vowed that he would "make it" before going into surgery.

The mechanical pump that made him the world's fourth artificial heart recipient was identical in design to devices manufactured by Salt Lake City's Symbion Inc. that had been implanted earlier in three Americans.

But spokesmen for Symbion and the federal Food and Drug Administration said the heart implanted in Sweden was manufactured by a German subsidiary of the company, circumventing U.S. regulations that would have required FDA export approval before the operation.

Sweden has a more liberal approach to medical device research than the United States. Tanja Blanck, a spokesman for the Karolinska Hospital, said by telephone that "government permission was not necessary." A spokesman for the Swedish Embassy in Washington said that "we don't have that kind of strict regulation . . . . You have to ask the county councils for the money in order to do this sort of operation . But you don't have to apply centrally to the government for any kind of permit."

Artificial heart inventor Dr. Robert Jarvik, head of Symbion, flew to Sweden to observe the surgery at Karolinska Hospital, a prestigious facility linked with the Karolinska Institute, which awards the Nobel Prize for medicine.

Semb, 45, who has headed Karolinska's heart surgery clinic since last year, trained on animals in Salt Lake City for two weeks in March in the procedures involved with the Jarvik device. He had been engaged in discussions with the American company since last year, according to Symbion vice president Don Williamson. Semb has previously done heart transplants and reportedly once worked with heart transplant pioneer Christiaan Barnard in South Africa.

Semb is only the second surgeon to implant the device. Dr. William C. DeVries, now at the Humana Heart Institute in Louisville, implanted the first artificial heart in dentist Barney Clark in December l982. Clark lived for 112 days with the device.

The Swedish operation came one day after the second artificial heart recipient, William J. Schroeder, was discharged from the Humana Audubon Hospital, where he underwent surgery Nov. 25. Murray Haydon, who received a mechanical heart at Humana on Feb. 17, remains hospitalized in serious but stable condition.

Humana spokesmen said DeVries spoke with Semb by telephone early Monday morning and quoted DeVries as saying he was "looking forward to active collaboration with the team doing this historic first for Europe. I wish them congratulations and I am hopeful for their success." DeVries has FDA permission to do four more artificial heart implants under strict guidelines.