File photo shows Vice President Richard Cheney addressing at Arlington National Cemetery during Veteran's Day ceremonies in Washington, DC, November 11, 2007. Cheney, who has a history of heart problems, was found to have an irregular heartbeat during a doctor's visit on Monday morning, his office said. REUTERS/Joshua Robert

WASHINGTON (Reuters) - U.S. Vice President Dick Cheney, with a history of heart problems, was found to have an irregular heartbeat during a doctor’s visit on Monday and went to hospital for more evaluation, his office said.

Tests determined Cheney, 66, one of President George W. Bush’s closest advisers, had “atrial fibrillation, an abnormal rhythm involving the upper chambers of the heart,” said Megan Mitchell, his spokeswoman.

Cheney, who had gone to see his doctors because of a lingering cough from a cold, went to the hospital for further evaluation and, if required, will have an electric impulse to the heart delivered, a standard treatment, Mitchell said.

He would be sedated for the outpatient procedure and would be expected to return home on Monday night, she said.

Atrial fibrillation is a disorder becoming increasingly common. The heart’s two small upper chambers quiver instead of beating effectively and blood is not pumped completely out, so it may pool and clot, putting the person at risk of stroke.

Cheney survived four heart attacks before he became vice president. The last one, shortly after the November 2000 election, was considered mild.

More recently he was treated for a blood clot in his leg that was discovered after a trip to Asia and the Middle East.

He had his internal heart-regulating device, an implanted cardioverter defibrillator, replaced in July. The devices monitor the heart and shock it back into a normal rhythm if abnormal beating occurs.

Cheney also had surgery to treat abnormal blood vessels, or aneurysms, behind both knees in September 2005.