Clinton was expected to undergo surgery as early as tomorrow but probably Tuesday, said Democratic National Committee Chairman Terry McAuliffe, who said the former president was "upbeat" when he spoke to him by phone Friday.
He was to undergo triple or quadruple bypass surgery, said someone close to Clinton who requested anonymity.
Clinton's wife and daughter visited him in the hospital yesterday, and he had received 15,000 get-well messages relayed from the Web site of his foundation, a spokeswoman said.
Clinton was admitted to New York Presbyterian Hospital/Columbia on Friday after suffering chest pains and shortness of breath.
He had been scheduled to accompany his wife, Sen. Hillary Rodham Clinton, on a two-day tour of upstate New York. Instead, the senator and the couple's daughter, Chelsea, joined Clinton in New York City. Chelsea Clinton was seen entering the hospital yesterday afternoon, followed by her mother.
The operation is likely to curtail his campaigning for Democratic presidential candidate John Kerry. Clinton had agreed to campaign for Kerry in the two months before the Nov. 2 general election and has appeared at some Democratic Party events.
Kerry and President Bush sent best wishes to Clinton. Vice President Dick Cheney called Clinton yesterday from Las Vegas and said the former president "sounded good," a spokeswoman for Cheney said.
In a telephone call Friday evening to CNN's Larry King Live, Clinton said he was "a little scared but not much."
"I'm looking forward to it," Clinton said of the surgery. "I want to get back. I want to see what it's like to run five miles again."
On Friday at the Westchester Medical Center, near his home, he was given an angiogram, in which dye is used to detect blockages or narrowing of coronary arteries. The test revealed "multivessel coronary artery disease, normal heart function and no heart attack," said Dr. Anthony Pucillo, who performed the procedure.
Clinton, who turned 58 two weeks ago, blamed the blockage in part on genetics but also said he "may have done some damage in those years when I was too careless about what I ate."
As president, Clinton was an avid jogger, but he was known for his love of fast food.
He has appeared much slimmer since early this year, when he said he had cut out junk food, gone on the South Beach diet, which limits carbohydrates and fats, and started a workout regimen.
In bypass surgery, a new piece of blood vessel, usually taken from the patient's leg, is sewn into place on the outside of the heart to create a detour around a blockage.
Patients typically spend three to five days in the hospital and are encouraged to be fairly active right away.