Washington - Doctors examining US Vice President Dick Cheney discovered an abnormal rhythm in his heart Wednesday and ordered him to undergo treatment, the White House said. Cheney was diagnosed with a similar problem in November 2007 and received an electronic jolt to correct the rhythm.

Cheney, who has a history of heart problems, survived four heart attacks before he became vice president. The last one dated immediately after the November 2000 election was listed as mild.

Cheney had quadruple bypass surgery and operations to clear blocked arteries in 1988. He had been also fitted with a pacemaker in 2001. Its battery, which had been running slow, was replaced during a minor surgery in July.

He had surgery to treat abnormal blood vessels, or aneurysm, behind both knees in September 2005.

Atrial fibrillation is a condition experienced by 2.8 million Americans. The disease is affecting more individuals as the population age increases. Left untreated, the patient may suffer blood clotting in the brain, leading to a stroke.