The vice-president has a history of heart problems

Mr Cheney was given heart tests and was treated for water retention, during his four-and-a-half hour stay.

He was retaining fluids because of medication he was taking for a foot complaint, a hospital spokeswoman said.

Mr Cheney, 64, has a history of heart trouble. He suffered his fourth heart attack in 2000.

In 2001, he was fitted with a pacemaker.

He also had an operation to remove blood clots in his knees last year.

A hospital spokesman said Mr Cheney's foot complaint was not connected to the September 2005 operation on his knees or to his history of heart attacks, the Associated Press news agency reports.

An examination of electrical activity in Mr Cheney's heart had found nothing unusual on Monday, a statement from his office said.

It said he had been placed on a diuretic to help get rid of the fluids.