Hanson publicist Ken Philips told the Tulsa World Thursday that eldest brother Isaac Hanson was undergoing surgery for a pulmonary embolism at a Dallas hospital.

"He's still in surgery . . . We have a few more hours before we'll get any update," he said.

Isaac Hanson was taken to a hospital there early Wednesday morning after a performance there as part of the band's "The Walk" tour. He was complaining of severe chest and shoulder pain, said Philips.

Yesterday afternoon, youngest brother Zac Hanson told the Tulsa World that a blood clot had lodged in Isaac Hanson's arm and needed emergency surgery.

CNN has reported that he was transported to Baylor University Medical Center, and Dallas-Fort Worth television station KDFW reported that he was diagnosed with a pulmonary embolism, which occurs when a blood clot in the extremities breaks away and travels to the lungs.