WASHINGTON (Reuters) - U.S. Vice President Dick Cheney, who has a history of heart problems, was treated with an electric shock on Wednesday to resolve an abnormal heartbeat -- the second time in less than a year.

Cheney returned to his official residence and resumed his normal schedule after the procedure, said his spokeswoman Megan Mitchell.

“An electrical impulse was delivered to restore the heart to normal rhythm,” Mitchell said. “The procedure went smoothly and without complication.”

Cheney, 67, attended President George W. Bush’s morning daily security briefings and stayed at the White House working until being treated at George Washington University Hospital, a visit that lasted just under two hours.

Because of the heart problem, Cheney canceled a campaign appearance in Illinois for a Republican congressional candidate but called into a reception to express his support, his spokeswoman said.

Cheney, one of the most powerful vice presidents in U.S. history, had a similar heart problem in November and received an electric shock to restore a normal rhythm.

In July, he had his yearly routine physical examination and doctors gave him the all-clear.

Cheney has had four heart attacks, quadruple bypass surgery, two artery-clearing angioplasties and a procedure to implant a defibrillator. He had his most recent heart attack shortly after the 2000 election but it was considered mild.

The vice president had the defibrillator implanted in his chest in 2001 to help regulate his heartbeat.

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Bush told reporters while traveling in Michigan that he was confident Cheney would be fine. He said the vice president told him he was undergoing the procedure.

“He was confident, the doctors are confident, therefore I’m confident,” Bush said.

Cheney’s latest problem was atrial fibrillation, in which the two upper chambers of the heart beat quickly and irregularly. Because blood is not pumped completely from the heart’s upper chambers, it can pool and clot, raising the risk of a stroke.

About 15 percent of strokes occur in people with atrial fibrillation, according to the American Heart Association. Some 2.2 million Americans have this type of abnormal heart rhythm.