Cheney, 67, canceled a campaign event he was scheduled to attend Wednesday in Homer Glen, Ill.

"During a visit with his doctors this morning, it was discovered that the vice president is experiencing a recurrence of atrial fibrillation, an abnormal rhythm involving the upper chambers of the heart," said Megan Mitchell, a spokeswoman for the vice president.

The vice president's office said that after experiencing the problem, Cheney saw the White House physician.

"Later this afternoon, the vice president will visit George Washington University Hospital for an outpatient procedure to restore his normal rhythm," Mitchell said.

In November 2007, doctors had to administer an electrical shock to Cheney's heart to restore it to a normal rhythm. That irregular heartbeat, like this one, was determined to be atrial fibrillation, an abnormal rhythm involving the upper chambers of the heart. At that time, White House doctors discovered the irregular heartbeat when they were treating him for a lingering cough from a cold.

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.