Cardiac specialists say that former President Bill Clinton, who had stent surgery this afternoon at NewYork-Presbyterian Hospital after complaining about heart pains, will likely have a full recovery.
Clinton, who is 63, had quadruple bypass surgery at the same hospital in 2004 after angiography revealed significant blockages in four coronary arteries.
Six months later, Clinton had surgery to remove fluid and scar tissue from his left chest cavity.
"It's not all that unusual six years out from bypass surgery to require such a procedure," said Dr. Jon Resar, director of the Adult Cardiac Catheterization Laboratory at Johns Hopkins Hospital in Maryland.
Stent surgery is a "minimal" and fairly routine procedure that is done when the patient is awake under "twilight" sedation, said Resar, an interventional cardiologist. Clinton was most likely "relaxed and conversing with the [medical] team members."
Dr. Mark Apfelbaum and Dr. Michael Collins did the stent procedure on Clinton.
"This will hopefully permanently deal with the blockage," Resar told ABCNews.com.
"Across the board, there is an 80 to 90 percent chance this deals with the problem permanently," he said.
Clinton, known for his rigorous schedule -- "20 hours a day for 20 years," according to sources close to the former president -- just returned from a day trip to Haiti as part of his work as a United Nations special envoy to the earthquake-ravaged country.
"As we know, Clinton changed his diet and was on cholesterol-lowering medication," said Resar. "But stress does play a role. But blockages in these bypass grafts can occur despite the fact that someone makes dramatic changes in their lifestyle and does all the right things."
Though Clinton has been under increased stress in Haiti, it may have "brought it to the surface, but didn't precipitate" the event, he said.
He was taken to the hospital today after "feeling discomfort in his chest," and had two stents placed in one of his coronary arteries, according to a statement from Douglas Band, counselor to the former president.
What a Stent Procedure Means for Clinton
A stent is a small wire mesh tube that is inserted into an artery in order to prop it open, like a miniature scaffold. Surgeons use stents to improve blood flow to the heart muscle and relieve symptoms such as the chest pain that Clinton experienced. The procedure to place a stent is considered minimally invasive, as surgeons do not have to open up the patient's chest cavity in order to put it in.
Instead, doctors collapse the stent and fit it onto what is known as a balloon catheter -- a flexible tube with a balloon at the end which is threaded into the blocked artery. Once the stent is in position, doctors inflate the balloon, which causes the stent to expand and lock into place, propping the artery open.
Most of the stents that are used today are known as drug-eluting stents. As the name implies, these stents leach a drug into the artery in which they are placed in order to prevent it from closing back up.
Once a surgeon puts it in place, the stent is a permanent addition to the artery. In a matter of weeks, the inside lining of the artery grows over the metal surface of the stent.
Millions of people worldwide have at least one drug-eluting stent in their bodies, and according to the American Heart Association, stenting procedures are fairly common in the United States; currently about 70 percent of coronary angioplasty procedures also involve stenting.
Cardiologists said the idea that Clinton would have chest pains now is not surprising, considering his previous heart problems.
"Coronary disease is a chronic condition that is not 'cured' by bypass surgery," said Dr. Steven Nissen, chairman of Cardiovascular Medicine at the Cleveland Clinic. Nissen said that many patients develop chest pain within five to 10 years after their bypass operations.
Still, not all of these patients have chest pain that is severe enough to warrant a stent. "Probably only 10 to 20 percent will have significant enough symptoms to require stenting," said Dr. Fred Feit, associate professor of cardiology at New York University.
Clinton 'Tired' Following Haiti Trip
When the news first broke, ABC News' George Stephanopoulos reported that Clinton had been feeling "tired" and had been fighting a cold.
In the past, Clinton has been overweight and had a notoriously bad diet of fast food and donuts.
Just three years before his bypass surgery in 2001, Clinton's cholesterol level was high at 233 and his LDL, or "bad" cholesterol, was very high at 177, so he began taking Zocor, a statin drug, to lower it.
At some point, Clinton stopped taking Zocor, apparently on his own, according to a report in The New York Times.
But when he was admitted to NewYork-Presbyterian Hospital/Columbia University Medical Center on Sept. 3, 2004, for coronary bypass surgery, his LDL was still 114.
"The most important prognosisticator is what is going on in the muscle before the operation," said cardiologist Resar.
After Clinton's bypass surgery, "his function was completely normal and remains good," said Resar.
"What may have happened is one of the bypass grafts developed a blockage or became totally occluded [blocked] or a new blockage developed beyond where the the original bypass was inserted into the artery," he said.
The risks of these blockages are usually higher if the damage has occurred within the original bypass.
After the procedure, patients must take at least one blood-thinning agent, such as aspirin or clopidogrel, to reduce the risk of blood clots developing in the stent and closing off the artery. A few recent studies suggest that blood clots could develop more than a year after stent placement in the drug-eluting stents.
Doctors said Clinton would likely be discharged tomorrow and resume most of his actvitites.
Dr. Steven R. Bailey, president of the Society for Cardiovascular Angiography and Interventions, told MedPage Today that coronary artery disease is not a single event.
"Bypass surgery does work," he said, "but we're dealing not with an event, but a disease, and it does progress."
Bailey said Clinton paid attention to his symptoms and got quick medical attention, and, therefore, is a good model for others.
ABC News' Karin Halperin contributed to this report.