A team of doctors at the University of Michigan Medical Center performed the state's first artificial heart implant operation early Saturday, a university spokesman said.

The patient was listed in critical but stable condition Saturday afternoon, which is considered normal in the hours following such operations, said school spokesman Mike Harrison.At the family's request, no information was released on the patient. Federal guidelines require that artificial heart recipients be between the ages of 18 and 55.

Harrison stressed the operation is a temporary measure, not a permanent implant, designed to keep the patient alive until a donated heart can be located.

"It's just a bridge," he said. "It could be (replaced with a donated heart) today; it could be a month from now."

The five-hour operation was performed by a 13-member team led by Dr. Michael Deeb. Work was completed some time after midnight Friday, Harrison said.

Doctors implanted a Symbion J-7 heart, which is described as a modified version of the Jarvik device involved in many implant operations. Worldwide, more than 80 patients have received the Symbion J-7, he said.

Harrison said it is not possible to say precisely how long the artificial heart can last.

"The heart is very strong," he said. "It can last a long time. It depends on the patient and whether he can hold on."

The major risks with such an operation, he said, are infection and blood clots or air bubbles.

Harrison said there was no indication whether any of these problems had developed.

Generally, two types of patients are viewed as appropriate for such implants - those whose condition deteriorates rapidly while they are waiting for a donor and those who suffer a sudden, catastrophic heart problem.