Barney B. Clark swung his legs over the side of his hospital bed yesterday and stood up without assistance for the first time since he became the world's first recipient of a permanent artificial heart.

"I think his chances are good of going home," said William DeVries, the surgeon who implanted the plastic, metal and cloth device 19 days ago.

Even the pneumonia that set in last week has been cured. "There seems to be no infection anywhere," said DeVries.

"In fact, we are taking him off all the antibiotics."

After Clark put his feet on the floor and stood up alone, DeVries said, he was helped to a chair near the window of his room at the University of Utah Medical Center in Salt Lake City. He sat with his wife, Una Loy, and looked at the snow-covered Wasatch Mountains to the east.

DeVries declined to say when he thought the 61-year-old former resident of Des Moines, Wash., could leave the hospital and move into his new home in Salt Lake City. Clark, whose disease-weakened heart was about to fail when it was replaced by the artificial device Dec. 2, will be tethered for the rest of his life by two 6-foot-long air hoses to a mobile air pump that drives the artificial heart.

It was the first time DeVries had spoken at a press briefing since the implant. The official who usually briefs reporters, Dr. Chase Peterson, university vice president for health sciences, cautioned later that Clark's new heart "could blow a valve at any time. We're on uncharted ground here."

Since the initial surgery, Clark's progress has been set back by an air leak in his lungs, a major seizure apparently caused by chemical imbalances in his blood and a partial break in one valve of the artificial heart. But he has recovered from each, and his condition has been upgraded from "critical" to "serious."

Although Clark cannot speak because of a respirator tube in his throat, he joked with his daughter through sign language that his hospital stay felt more "like five years than three weeks." He sipped fruit juice and did some leg exercises on the edge of his bed.

Asked if he considered the operation a success, DeVries, 38, said, "From a research standpoint, it is an extreme success . . . . But if you determine your success by the patient's quality of life, he's still got a ways to go before I think he will feel it is a success. Although, I think from the humanitarian aspect he has accomplished a lot and I think he will feel good about that.

"I will be happy when his life is better than it was before surgery."

The surgeon described how the artificial heart, designed by Dr. Robert Jarvik to pump at any speed desired, aided doctors in treating Clark's several post-operative ailments. Clark's kidneys failed a few days after the implant, and when all traditional means of reviving them failed, "we were able to just walk over and turn up the heart machine and literally pump out his kidneys." Without the artificial heart, doctors would have had to use a kidney dialysis machine.

When the valve on the heart partially failed Dec. 14, Clark's blood pressure dropped suddenly. But doctors were able to turn down the machine to prevent the heart from overpumping until they could operate and replace the defective part.