Artificial-heart recipient Murray P. Haydon has almost completely recovered from a stroke that left him unresponsive and partially paralyzed Monday night, doctors said today.

Haydon, 58, whose recovery has been slow since he received the heart Feb. 17, had regained enough strength to have his first workout on a stationary exercise bicycle over the weekend at Humana Hospital Audubon.

On Monday, he became extremely drowsy and weak on his left side. Doctors returned him to the respirator that has assisted his breathing intermittently for more than two months because of a lung ailment, and he was given steroids Monday night to reduce swelling in the brain.

This morning, however, he was alert, able to move his hands and feet and was "95 to 98 percent recovered," neurologist Dr. Gary Fox said.

The stroke apparently was caused by a tiny clot or piece of plaque lodged in an artery on the right side of the brain, but blood is making its way around the obstruction, Fox told reporters today. Dr. William C. DeVries, who implanted the heart, acknowledged that strokes have been "a common complication" among artificial-heart patients.

But he maintained that, in order to provide an accurate assessment, more patients must undergo the procedure.

"When we get more numbers, we'll decide what the true stroke incidence is. This may be the last one that has it. It may not be," he said.

DeVries' other living artificial-heart patient, William J. Schroeder, 53, suffered a major stroke 18 days after receiving a new heart in November and incurred severe speech and memory loss.

In May, one month after being discharged from the hospital to an apartment across the street, he suffered a second stroke that left him with limited awareness of his surroundings and an inability to talk.

DeVries also said that an unidentified patient who received an artificial heart in Sweden two months ago has sustained "some neurological problems," but he declined to elaborate.

The stroke problem illustrates a medical team's problem in finding the balance between administering too little anticlotting medicine, which invites possible strokes, and administering too much, which can cause excessive bleeding.

Haydon required a second open-heart operation several days after his implant to stop bleeding from a tiny hole left by a needle-thin monitoring line removed from a remnant of his natural heart.

Jack C. Burcham, DeVries' fourth patient, died in April, 10 days after receiving a Jarvik-7 heart when blood pooled in his chest, squeezing shut a chamber of his natural heart, to which the device is attached. Burcham also underwent a second open-heart operation to stem massive bleeding.

Haydon has received multiple transfusions, which eventually resulted in a lung problem called adult respiratory distress syndrome, leaving him unable to breath without a respirator.

DeVries said that he has no plans to change Haydon's anticoagulation regimen, since no research suggests an alternative and that he will continue to seek more subjects for his experiments. "If we get a good patient, we would go ahead," he said.

The attitude of Haydon's family, he said, "is that he would be dead . . . if he hadn't had the heart, and any moment they have has been worthwhile to them."

In contrast, Schroeder has shown little improvement since readmission to the hospital. When Schroeder's new grandchild was christened Sunday in his hospital room, the patient appeared to recognize family members and wept when he held the baby.

"He does have peripheral movement of his hands. He'll itch his nose and try to comb his hair and those sort of things," DeVries said.