Nov. 26 (Bloomberg) -- Vice President Dick Cheney was found to have an irregular heartbeat during a medical evaluation this morning and is undergoing further testing at George Washington University Hospital, his spokeswoman said.

Cheney, who has had four heart attacks, has an ``abnormal rhythm involving the upper chambers of the heart,'' spokeswoman Megan Mitchell said in an e-mailed statement. It was discovered during an evaluation conducted because the vice president had a ``lingering cough from a cold.''

Cheney, 66, left the White House about 5:00 p.m. for the hospital, and doctors may treat him on an outpatient basis by applying an electrical impulse to his heart to restore normal heartbeat. This is ``a standard treatment,'' Mitchell said. The vice president is expected to return home tonight, she said.

Cheney's four heart attacks occurred before he became vice president. He also has had quadruple bypass surgery, two angioplasties and surgery on his legs to repair an aneurysm. He was treated in March for a blood clot in his lower left leg.

In July, the defibrillator implanted in the vice president's chest to regulate his heartbeat was replaced with a new one with a fresh battery. The original was placed in Cheney's chest in June 2001, six months after he became vice president.

The condition that doctors are evaluating this afternoon is called atrial fibrillation, which the American Heart Association says affects three to five percent of people over 65. It occurs when the heart's two upper chambers quiver instead of beating regularly. About 15 percent of strokes occur in people with the condition, according to the association's Web site.

To contact the reporter on this story: Holly Rosenkrantz in Washington at hrosenkrantz@bloomberg.net.

Last Updated: November 26, 2007 17:45 EST