Sen. Robert Byrd, the longest-serving member of Congress, was admitted to a Washington-area hospital last week and is considered "seriously ill," according to a statement released today by his office.

Byrd, 92, was admitted to the hospital after "suffering from what was believed to be heat exhaustion and severe dehydration as a result of the extreme temperatures," according to the statement. "However, upon further examination by his doctors, other conditions have developed which has resulted in his condition being described as 'serious.' "

In November, Byrd broke the record for congressional service that had been set by Democrat Carl Hayden of Arizona, who served in the House and Senate from 1912 to 1969, according to the Associated Press. Byrd began his career in Washington in 1952 with his election to the House. His elevation to the Senate came six years later.

Updated at 3:52 p.m. ET: Byrd, a Democrat, spent several weeks in the hospital in June 2009 for an infection. At the time, Democratic Sen. Jay Rockefeller, also from West Virginia, described Byrd's health as frail but said Byrd was able to attend key votes in the Senate.

Depending on Byrd's prognosis, that may be more difficult this time. This coming week is the last work period before the Senate goes on a week-long break for the July 4 holiday. Senate Democrats hope to move their financial regulation legislation to a final vote before the break.

(Posted by John Fritze)