SOUTH BEND, Ind. (AP) — South Bend’s mayor was hospitalized after undergoing an unexpected surgery, according to his office.

The surgery on Mayor James Mueller was performed Friday by Memorial Hospital’s cardiothoracic team. A statement from the mayor’s office said he was expected to be released from the hospital in a few days and make a full recovery.

No details about Mueller’s medical problem were released, but cardiothoracic surgeons specialize in procedures involving the heart, lungs and other organs in the chest.

Mueller, who became the city’s mayor in January 2020, turned 40 on Wednesday.

Mueller previously was a top aide to then-Mayor Pete Buttigieg, who endorsed Mueller as his successor in the 2019 city election while Buttigieg was seeking the Democratic presidential nomination. Buttigieg is now President Joe Biden’s transportation secretary.