White House spokesman Ken Lisaius said on Saturday that Cheney's symptoms were related to a cold that he is battling.

"He experienced some shortness of breath Saturday morning and has had a bad cold, which could be the cause for the shortness of breath," Lisaius said.

But Lisaius added that Cheney wanted to take "every precaution" so was having the symptoms checked out. 

Cheney, 63, underwent angioplasty in November 2000 after suffering his fourth heart attack since 1978.

He had a cardioverter defibrillator implanted in June 2001 following treatment for cardiac troubles after entering office with Bush in January 2001.

The device, implanted just beneath Cheney's left collarbone, can administer electric shocks to slow a potentially dangerous racing heartbeat or speed up an excessively slow one.