Anthony Mandia, the nation's eighth artificial-heart recipient, suddenly deteriorated to critical, unstable condition yesterday, slipping in and out of consciousness after what had looked like a quick recovery from his implant last Friday.

The new Pennsylvania State University heart that Mandia received was intended to be a temporary measure until a human heart could be found. One was located Monday, but it failed before a transplant team could transport it to Hershey, Pa., where Mandia, 44, is hospitalized.

Mandia, a former city clerk in Philadelphia, was the first patient to receive the artificial heart called the Penn State heart, designed specifically to avoid strokes and similar complications that have plagued previous artificial heart-implant patients.

Though some of Mandia's symptoms were similar to those of a stroke, Dr. John W. Burnside, medical spokesman and associate vice president of Penn State's Hershey Medical Center, said that the medical team saw none of the brain damage usually found when a stroke shuts off circulation to a portion of the brain.

Mandia was recovering rapidly from the implant and was out of bed Monday afternoon, but by 3 a.m. yesterday he had slipped into a stupor, unable to talk or respond to prompting.

Burnside said that at the worst moments, in the early hours yesterday morning, Mandia could not be aroused except by "painful stimuli."

Later yesterday Mandia was improving. His incoherent sounds gave way to understandable words and short conversation. Burnside said Mandia began to "lighten up" and told his brother: "Hi, Ernie. How you doing? See if you can get me something to eat."

But yesterday afternoon, as soon as prompting talk was stopped, Mandia quickly fell back into a stupor.

Doctors at Hershey do not know the cause of Mandia's problems, Burnside said, and there is no evidence on whether the device itself could have caused the problems.

Doctors now say the most likely explanation is that they have been caused by spasms in the brain's blood vessels. The spasms could be related to an old injury, a gunshot wound to the head Mandia received when he was a youth.

Mandia's brain may have reacted in an unexpected way, producing a seizure, they said. Or possibly the antiseizure drugs he has taken since the injury were involved; a low dose of the medication caused a 30-minute episode of slurred speech on Sunday.

Doctors don't believe the vasospasms are life-threatening, Burnside said. Mandia remains on the urgent list for a transplant and if a heart becomes available, doctors will then decide whether his condition will allow the operation to proceed.

Three hours before Mandia's condition changed on Monday, Hershey's transplant team received word from the Delaware Valley Transplant Program that a donor heart had been found.

But when the Hershey team arrived that night to pick up the heart, it had failed.