Mr. Clinton was expected to undergo surgery as early as Monday but probably Tuesday, said Democratic Party Chairman Terry McAuliffe, who said the former president was "upbeat" when he spoke to him by phone Friday.
"I thanked him for getting the Democrats back on the front page, and he told me that's about as far as he's willing to go," McAuliffe said Saturday. "I said I needed him out on the campaign trial as soon as possible, and he said as he soon as he recuperates he'll be ready to go."
He was to undergo triple or quadruple bypass surgery, according to a person close to Mr. Clinton who requested anonymity.
Mr. Clinton's wife and daughter visited him in the hospital Saturday, and he had received 15,000 get-well messages relayed from the Web site of his foundation, a spokeswoman said.
One message posted on the Web site Saturday read: "I'm having an awfully hard time imagining anything big enough to block a heart as large and generous as yours, but I hope you have the best surgeons in the country working on it."
Another, from a self-described "Reagan Democrat" said: "While I did not vote for President Clinton, nor agreed with a lot of his points of view, I always liked him. ... In March of 2002, I underwent quad bypass surgery, so I know what he will going through in the coming hours, days, and months. My prayers are with him."
Mr. Clinton was admitted to New York Presbyterian Hospital/Columbia on Friday after suffering chest pains and shortness of breath.
The surgery will be performed by New York Presbyterian Chief of Cardiac Surgery Craig Smith.
He had been scheduled to accompany his wife, Sen. Hillary Mr. Clinton, on a two-day tour of upstate New York. Instead, the senator and the couple's daughter, Chelsea, joined Mr. Clinton in New York City. Chelsea Clinton was seen entering the hospital Saturday afternoon, followed by her mother.
The operation is likely to curtail his campaigning for Democratic presidential candidate John Kerry. Mr. Clinton had agreed to campaign for Kerry in the two months before the Nov. 2 general election and had already appeared at some Democratic Party events.
CBS News political analyst Craig Crawford said Mr. Clinton might still be helpful to the Kerry campaign, with the drama of his surgery adding to his effectiveness. "My guess is Bill Clinton campaigning from a hospital bed is better than a dozen healthy politicians on the stump," Crawford said on The Saturday Early Show."
Both Kerry and President Bush sent best wishes to Mr. Clinton. Vice President Dick Cheney called Mr. Clinton on Saturday 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," Mr. Clinton said he was "a little scared, but not much."
"I'm looking forward to it," Mr. Clinton said of the surgery. "I want to get back. I want to see what it's like to run five miles again."
"Let me just say this," Mr. Clinton added, "Republicans aren't the only people who want four more years here."
Mr. Clinton first went to a hospital Thursday after suffering chest pains and shortness of breath, his office said in a statement.
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.
Mr. 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, Mr. Clinton was an avid jogger but he also 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" that 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.