US Vice-President Dick Cheney has a blood clot in his leg and is being treated with blood-thinning medication, his office has said.
Mr Cheney has a long history of heart trouble
He experienced discomfort in his lower left leg on Monday morning and had medical tests. He returned to work after the examination.
He is to be treated with blood-thinning medication for several months.
Mr Cheney, 66, has a history of cardiac problems. He has suffered four heart attacks and has a pacemaker.
He had quadruple bypass surgery in 1988 after his third heart attack.
He also had an operation to remove blood clots in his knees in 2005.
DICK CHENEY'S HEALTH
Four heart attacks between 1978 and 2000
Quadruple bypass surgery in 1988
Fitted for pacemaker to regulate heartbeat in 2001
Operation to remove blood clots in 2005
Mr Cheney recently returned to Washington after long flights to Japan, Australia, Pakistan and Afghanistan.
Blood clots - or deep vein thrombosis (DVT) - are often associated with long-distance flying because of the reduced air pressure and oxygen levels, and the long periods of inactivity and dehydration which can occur on planes.
Clots themselves are not life-threatening but can be dangerous if they become wedged in the lungs or other organs, which can in severe cases be fatal.