Cheney, left, has had a bad cold, his spokesman said

Mr Cheney was admitted earlier on Saturday after experiencing breathlessness.

A spokesman said he was undergoing tests on the recommendation of doctors.

Mr Cheney, 63, has a history of heart attacks. He had his fourth heart attack at the end of 2000 and in June 2001 he was fitted with a pacemaker.

"He has a bad cold, which could be the cause for the shortness of breath," spokesman Ken Lisaius said.

Mr Cheney was said not to be experiencing any chest pains - a common symptom of heart attacks.

Tests 'normal'

Mr Cheney voluntarily attended the George Washington University Hospital - a few blocks from the White House - after experiencing shortness of breath at about 1100 local time (1400 GMT).

He did not travel by ambulance.

Three hours later, he left, smiling and waving to reporters and accompanied by his wife Lynne.

Mr Cheney's pacemaker, which can give a read-out for the last three months, showed no irregularities, a spokeswoman for the vice-president told the Associated Press.

She also said an electrocardiogram had showed nothing abnormal.

Cheney campaigned hard, often accompanied by his wife Lynne

Earlier, officials stressed Mr Cheney's tests had been solely precautionary.

Mr Cheney has for the past week been nursing a cold he picked up on his annual hunting trip to South Dakota last week.

Before the latest US presidential election campaign Mr Cheney insisted that he was well enough to run again.

He kept to a frantic schedule during the campaign - even making a trip of just a few hours to Hawaii. Correspondents suggest he might now be feeling the after-effects.

Mr Cheney had an annual heart check-up last May, when doctors determined that the pacemaker had never been needed to assist his heart, AP said.

The device is designed to regulate his heartbeat automatically, should it excessively speed up or slow down.

Mr Cheney gave up smoking after his fourth heart attack, AP reported, exercises daily and takes cholesterol-lowering medication.