Sen. Daniel Inouye (D-Hawaii) has been hospitalized in order to allow doctors to monitor his oxygen intake.
Inouye, 88, released a statement that said he planeed to return to the Senate as soon as his doctors allow it.
Inouye, the chairman of the Appropriations Committee, is also the president pro tempore of the Senate, making him third in line after the vice president and House Speaker in line for the presidency.
Inouye is receiving care at Walter Reed hospital in Bethesda, Md.
Aides said that Inouye's breathing troubles are likely related to misdiagnosed cancer surgery he underwent in the 1960s, in which a large portion of his left lung was removed.