Former United States vice-president Dick Cheney, who has had five heart attacks since 1978, has been admitted to a Washington hospital.
A statement issued by his office says Mr Cheney, who was vice-president under the former president George W Bush, did not feel well and went to his doctors' offices.
He was taken to hospital for further tests and is not expected to be discharged until after the weekend.
Mr Cheney has had a long list of health scares, including quadruple bypass surgery and two artery-clearing angioplasties. In 2001 he was fitted with a pacemaker.
He has also twice been treated with electrical shocks for atrial fibrillation, an abnormal heart rhythm that places him at risk of a stroke, and in 2005 underwent surgery for an arterial aneurysm on the back of each of his knees.
Mr Cheney became one of the most powerful vice presidents in US history and has remained on the political scene since leaving office, fiercely criticising President Barack Obama, a Democrat.