An official told ABC News that Clinton's ailment seemed more like "discomfort ... something wasn't right" rather than a health "crisis."
A friend of the former president's said that he had been suffering from a cold and had been worn out from his trip to Haiti on Feb. 5. Another source who was with Clinton in Haiti told ABC News that he "looked really tired, exhausted and pale ... like he didn't sleep at all" during the Haiti trip.
It was Clinton's second trip to Haiti since the January earthquake, and as the United Nations special envoy for Haiti he met with Haitian leaders and helped coordinate international quake assistance.
Clinton, known for having a weakness for fast food during his years in the White House, underwent his complicated bypass procedure on Sept. 6, 2004, after an angiogram showed that his heart had multiple lesions. Clinton had taken himself to a hospital in Westchester, N.Y., a few days earlier after experiencing mild chest pain and shortness of breath.
The then-Sen. Hillary Clinton, D-N.Y., was at the New York State Fair in Syracuse, N.Y., when she learned of her husband's condition and immediately rushed to his side.
"His doctors asked him to come back early this morning for some additional tests, and as a result of those additional tests … they did advise him to have bypass surgery and to do it as soon as he could," Hillary Clinton said. "He's in excellent hands and he's at one of the best hospitals in the world."
In Clinton's first interview after his surgery, he told ABC's Diane Sawyer that he had visions that "clearly connoted death" while he was on the operating table.
"I saw like dark masks crushing, like death masks being crushed, in series, and then I'd see these great circles of light and then like Hillary's picture or Chelsea's face would appear on the light, and then they'd fly off into the dark," he told Sawyer.
Clinton added, "I'll never get tired of living. But I think it's a great waste of time to sit around in morbid fear of a fate that we all have to share."
In spring 2005, Clinton told ABC News that even after two surgeries, he "feels great."
"The pain is gone," said Clinton. "I can now pretty well do whatever I need to do."
Clinton underwent an additional surgery in March 2005 to remove scar tissue that had developed after the quadruple bypass surgery.
During a humanitarian trip to Liberia In 2008, Clinton said his "heart thing" had helped to "really change me."
"I think surviving that heart thing and then doing this work and being so inspired by people like this has really changed me, in a way," he told ABC News.
ABC News' Martha Raddatz and Kate Snow contributed to this report