The building, which is an over 20,000-square-foot landmarked mansion on the Upper East Side, was built in the early 20th century as a family house.

50 East 69th Street.

In 1979, the plastic and reconstructive surgeon James W. Smith bought it and converted it to medical offices and operating rooms. Since 1988, Dr. Smith’s Center for Specialty Care has been the only tenant in the building. Currently, it holds a 5-year lease, according to Massey Knakal.

On the current residential market, the mansion might reach a value of around $40 million, said Massey Knakal Capital Services’s Director Morris Betesh. “The $8 million refinanced an existing balance of approximately $6.5 million,” Mr. Betesh said. Excess proceeds from the loan financed new medical equipments and building upgrades, he added.

The lender was People’s United Bank, according to public records. The loan was fixed for ten years at 3 percent with the first two years interest only. The new interest rate on the loan was over 4 percent less than the prior rate.

“This is a very specialized asset,” said Mr. Betesh. He added that “lenders like this business model” and that the interest rate the financing came in at—3 percent—“is indicative of the low risk associate with the business model.”