George W. Bush’s recent heart problems were far more dangerous than generally believed — potentially life-threatening, in fact.

Sources familiar with the former president’s medical situation told National Journal that a major blockage in a coronary artery discovered during Bush’s annual physical exam in August had almost completely shut off blood flow to one of his heart chambers.

“He was more than 95% occluded,” an authoritative source said. “With a blockage like that in a main artery you’re supposed to die. He was pretty lucky they caught it.”

Dr. Jonathan Reiner, an interventional cardiologist at George Washington University who has treated former Vice President Dick Cheney but was not involved in Bush’s care, noted that a blockage of that magnitude wouldn’t necessarily be fatal in all patients but is a very serious situation requiring prompt treatment.