The attorney for Khaled Dumeisi says the 61-year-old has a history of heart trouble and blood clots.
Attorney James Fennerty says Dumeisi was taken to Rush Presbyterian St. Luke's Medical Center on Friday night.
Federal prosecutors contend Dumeisi was paid to spy on Iraqi opposition leaders in this country.
He is charged with serving as the agent of a foreign government without registering, lying to an immigration official and lying to a federal grand jury.
He had been held in the federal government's Metropolitan Correctional Center since his arrest on July 9.