WASHINGTON -- Vice President Dick Cheney experienced an abnormal heartbeat Wednesday morning and, upon the advice of White House doctors, went to the hospital for a procedure to "restore his normal rhythm."

Vice President Dick Cheney, center, applauds as President Bush, right, speaks before signing the United States-India Nuclear Cooperation Approval and Nonproliferation Enhancement Act during ceremony in the East Room of the White House in Washington, Wednesday, Oct. 8, 2008. Standing behind them on stage are from left to right, Secretary of State Condoleezza Rice, Energy Secretary Samuel Bodman, and Indian Ambassador to the U.S. Ronen Sen. (AP Photo/Pablo Martinez Monsivais) (Pablo Martinez Monsivais - AP)

For the 67-year-old Cheney, who canceled a campaign event he was to attend later Wednesday in Illinois, it will be the second time in less than a year that he will have the outpatient procedure _ which consists of an electric shock.

The vice president's office said that after experiencing a problem, Cheney saw the White House physician. It was discovered there that he was experiencing a recurrence of atrial fibrillation, an abnormal rhythm involving the upper chambers of the heart, said Megan Mitchell, a Cheney spokeswoman.

As a result, Cheney went to George Washington University Hospital in the afternoon, Mitchell said. Cheney remained at the White House until time for the procedure, and participated in regular morning briefings with President Bush, among other duties.

Cheney told Bush of his condition. The president responded "like he would with any friend," said spokesman Tony Fratto, by wishing the vice president well and telling him to "go and make sure the doctors do what they need to do."

Later, in Ada, Mich., Bush told reporters that Cheney is "going to be fine."

"He said he was confident, the doctors are confident, and therefore I'm confident," Bush said.

Cheney also experienced atrial fibrillation in November 2007, and doctors also administered an electrical shock then in a treatment that took about 2 1/2 hours. That irregular heartbeat was discovered while White House doctors were treating the vice president for a lingering cough from a cold.

Dr. Zayd Eldadah, director of cardiac arrhythmia research at Washington Hospital Center in Washington, said it's not unusual for Cheney to have another such episode. An estimated 2.8 million Americans have atrial fibrillation, the most common type of irregular heartbeat and one that is not life-threatening in itself.

"This kind of rhythm problem generally does keep coming back over time," said Eldadah, who is not involved in Cheney's care. "The natural history of atrial fibrillation in people who have heart disease and are older is that it keeps coming back, and generally comes back more frequently."

The main risk from atrial fibrillation is not that Cheney will have another heart attack, but that he could eventually have a stroke if the rhythm problem is not treated.

Atrial fibrillation, also called A-fib, causes the upper chambers of the heart to quiver, instead of pump. As a result, some blood can pool in the heart. When blood settles, it tends to clot. And if those clots are then pumped out to the body, they can lodge in tiny blood vessels in the brain _ causing a stroke.

The procedure Cheney was expected to undergo Wednesday afternoon is like resetting a computer, Eldadah explained. The vice president will be sedated, and an electrical charge will be delivered to his heart. "The heart will be turned off and on to reset it," said Eldadah. "It's a quick fix to restore normal rhythm."

If the procedure doesn't work, patients typically are put on blood thinners to prevent clotting.

"Atrial fibrillation in patients like Vice President Cheney is not a source of great worry or alarm," said Eldadah. "It's very treatable."

Cheney has had four heart attacks, starting when he was 37 years old, and many related doctor and hospital visits over the years since. He has had quadruple bypass surgery and two artery-clearing angioplasties. In 2001, he had a special pacemaker implanted in his chest. The pacemaker's battery was replaced last year, and then the entire device was replaced.

In 2005, he had surgery to repair an arterial aneurysm on the back of each knee.

In his checkup in July, doctors said Cheney's heart was beating normally for a man of his age and health history.

The campaign event Cheney will miss is for Marty Ozinga, a wealthy suburban concrete company owner. Ozinga is running for the House against Democrat Debbie Halvorson, a high-ranking Illinois state senator.

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Associated Press Writer Ricardo Alonso-Zaldivar in Washington contributed to this report.

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