US Vice-President Dick Cheney has successfully undergone treatment to correct an abnormal heart rhythm, his spokeswoman has said.
Mr Cheney, 67, received an electric impulse which was administered without complication at the George Washington University Hospital.
He later resumed his normal schedule, but was forced to cancel a planned political event in Illinois.
Mr Cheney has had four heart attacks and quadruple bypass surgery.
He has undergone several operations to clear blocked arteries and was fitted with a pacemaker seven years ago.
"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 the spokeswoman, Megan Mitchell.
"An electrical impulse was delivered to restore the heart to normal rhythm," Ms Mitchell added later.
Stroke risk
The vice-president has been treated for the condition before. In July 2007, he received cardioversion - a procedure that involves the delivery of an electric impulse to the heart.
In 2005, Mr Cheney underwent surgery to repair damaged arteries in his knees and in 2007 he had an operation to replace the battery in his pacemaker.
However, doctors gave Mr Cheney a clean bill of health at his last routine medical check-up in July this year.
About 2.8 million Americans suffer from atrial fibrillation, the most common type of heartbeat irregularity.
The condition prevents the heart from pumping blood effectively around the body, increasing the risk of blood clots and strokes.
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