Two well-known, independent cardiac surgeons are joining the University of Pittsburgh Medical Center Tuesday and will no longer see patients at rivals Jefferson Regional Medical Center and The Western Pennsylvania Hospital's Forbes campus come October.

Dr. Venkat Machiraju and Dr. Claudio Lima will work from UPMC Shadyside and UPMC Mercy under three-year contracts, said UPMC spokeswoman Maureen McGaffin.

In a joint letter to other doctors, Dr. Machiraju and Dr. Lima said the transition would begin July 1 and the new affiliation would "improve the financial security of our practice, provide us relief from its administrative burdens, and most importantly, give us better on-call coverage as we participate in a larger practice." They pledged to care for existing patients at Jefferson Regional and West Penn through September but would not see new patients at those hospitals.

Their move from RAJ Cardiovascular Associates to UPMC is part of a trend of private doctors choosing the safety of a large health system over the vulnerability of running an independent medical practice. Rising costs and declining reimbursements are the cause of this shift, said Allegheny County Medical Society Executive Director Jack Krah.

"The pressures are there for them to become part of a bigger organization," he said.

Jefferson Regional Chief Executive Officer Tom Timcho said Dr. Machiraju's group was responsible for one-third of the hospital's 455 open-heart operations during the fiscal year ended June 30, 2007. But he is confident the Pleasant Hills hospital can retain that volume, despite Dr. Machiraju's new employment with UPMC. "We are sorry to see Dr. Machiraju leave," he said, "but there are more than sufficient resources to continue serving the patients in the Jefferson Medical service areas."

"This," he added, " is a unique situation when another organization like UPMC hires a doctor and has them resign from our staff. I can't remember a time when that has happened before."

Neither Dr. Machiraju or Dr. Lima could be reached for comment. Both are based at UPMC Shadyside. Dr. Machiraju will become professor of surgery and director of the cardiovascular unit at UPMC Shadyside, while Dr. Lima will be assistant professor of surgery. With the additions, UPMC has 40 cardiothoracic surgeons and fellows.