[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2010/images/06/27/art.byrd0627.cnn.jpg caption="Sen. Robert Byrd, age 92, is the longest-serving Congress member in history."]
Washington (CNN) - Sen. Robert Byrd, the 92-year-old Democrat from West Virginia who is the longest-serving Congress member in history, has been hospitalized in serious condition, his office said Sunday.
Byrd was admitted to a Washington area hospital last week and his condition is "seriously ill," according to the statement by his office.
Initially thought to be suffering from heat exhaustion and severe dehydration, Byrd was expected to remain in hospital for "not more than a few days," the statement said.
"However, upon further examination by his doctors, other conditions have developed which has resulted in his condition being described as 'serious,' " the statement concluded.
Updated: 3:35 p.m.