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 Cheney has a history of heart problems, including four heart attacks, starting at age 37.
When doctors rule out an immediate heart attack, the next step in evaluating chest pain usually is an X-ray exam called an angiogram to help uncover the cause. Doctors inject a dye that will highlight narrowed arteries leading to the heart.
Blockages aren't the only explanation for chest pain. But Cheney had bypass surgery in 1988, as well as two later angioplasties to clear narrowed coronary arteries, and bypasses tend to last about a decade before the rerouted blood vessels start to clog.
In 2001, he had a special pacemaker implanted in his chest. In addition, doctors in 2008 restored a normal rhythm to his heart with an electric shock. It was the second time in less than a year that Cheney had experienced and been treated for an atrial fibrillation, an abnormal rhythm involving the upper chambers of the heart.
The former vice president has kept a high profile since leaving the White House. He has sparred with the Obama administration over plans to close the U.S. detention facility for terror suspects at Guantanamo Bay, Cuba, and hold the trials of several high-profile detainees in civilian courts rather than military tribunals.
He made a surprise appearance last week at the Conservative Political Action Conference, where he accompanied his daughter Liz. He was greeted with chants of "Run, Dick, Run," but said "I am not going to do it."
Among his extensive government service, Cheney served as defense secretary under President George H.W. Bush.
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