Washington (CNN) -- Former Vice President Dick Cheney was hospitalized Monday with chest pains, according to his office.
Cheney, 69, is resting comfortably at George Washington University Hospital, and his doctors are evaluating the situation, his staff said in a statement.
A family source told CNN that Cheney will be kept in the hospital overnight for observation and additional tests. Another source said Cheney is up and in touch with his family and friends.
CNN's chief medical correspondent Sanjay Gupta called Cheney's mobility "a good sign."
"If he's up and walking around, talking to friends ... that probably means he's not in the intensive care unit," he said. "They're not doing active procedures on his heart. He's not on a breathing machine or anything like that. No one ever said he was. It's obviously a good sign."
Cheney has a long history of heart problems. He has suffered four heart attacks dating to 1978, when he was 37. He had his second in 1984 and a third in 1988 before undergoing quadruple bypass surgery to unblock his arteries. His fourth heart attack happened in November 2000, after he was elected vice president. At that time, doctors inserted a stent to open an artery.
Doctors in 2001 implanted a heart monitoring device to keep track of his heart rhythm and slow it down if necessary. In 2008, he underwent a procedure to restore his heart to a normal rhythm after doctors found he was experiencing a recurrence of atrial fibrillation.
Cheney served under former President George W. Bush from 2001 to 2009. He has been a vocal critic of the current administration since he left office, most recently appearing on ABC's "This Week," where he railed against President Obama's policies on terror and the Iraq war.
He has accused the Obama administration of failing to treat the fight against terrorists as war, citing the decisions to give 9/11 suspect Khalid Sheikh Mohammed a civilian trial, give the failed Christmas Day airline bombing suspect the privileges of the U.S. criminal justice system, and shut down the U.S. military prison at Guantanamo Bay, Cuba.
Cheney also served in the administrations of former Presidents Richard Nixon, Gerald Ford and George H.W. Bush.
CNN's John King contributed to this report.