Vice President Dick Cheney was expected to undergo more testing at George Washington University Hospital after it was discovered Monday that he had an irregular heartbeat.

The condition was detected after the vice president consulted with doctors over a lingering cough.

"During examination, he was incidentally found to have an irregular heartbeat, which on further testing was determined to be atrial fibrillation, an abnormal rhythm involving the upper chambers of the heart," said Cheney's spokeswoman Megan Mitchell.

According to the American Heart Association (AHA), the disorder can be found in about 2.2 million Americans. When a person suffers from atrial fibrillation, the heart's two small upper chambers (the atria) do not beat effectively. Blood isn't pumped out completely and may pool or clot. That is when things can get take a dangerous turn.

"The major danger is stroke, which occurs because a clot forms in the upper chamber and that clot can become dislodged and travel in the circulation," said Dr. Jonathan Steinberg, professor of medicine at Columbia University and chief of cardiology at St. Luke's and Roosevelt hospitals. "If that clot goes up to brain, it can cause a stroke."

The likelihood of developing atrial fibrillation increases with age. Three to five percent of people over 65 have atrial fibrillation.

"It's the most common prolonged arrhythmia there is," said Steinberg. "At his age, about one in 20 people have atrial fibrillation."

There are several treatments, noted Steinberg, including cardioversion.

"I would imagine that they are going to monitor him with recording devices," he said. "They'll check his heart function again, put him on blood thinners, and depending on what pattern, he might undergo a shock procedure (cardioversion) to restore his rhythm to normal."

Cheney, 66, has a history of heart problems. He's had a total of four heart attacks — the first one in 1978 when he was only 37-years-old, and the most recent in 2000. He's undergone quadruple bypass surgery, two angioplasties, and an operation to implant a special pacemaker in his chest. He was also put on blood thinners in March of this year.

The Associated Press contributed to this report.