An angiogram showed that Clinton, who turned 58 two weeks ago, had significant blockage in his heart arteries but did not suffer a heart attack, a doctor who performed the test told The Associated Press.
He awaited the operation at New York Presbyterian Hospital/Columbia, in upper Manhattan, not far from his Harlem office.
Clinton's wife, Sen. Hillary Rodham Clinton, said Friday evening that the former president would have surgery early next week and that no further information about his condition would be released until the operation is finished.
``I wanted to report to you that my husband is doing very well,'' she said outside the hospital, where the former president is being treated. ``He's in great humor. He's beating all of us at cards and the rest of the games we're playing.''
In bypass surgery, a new piece of blood vessel, usually taken from the patient's leg, is sewn into place 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.
Clinton had agreed to campaign for Democrat John Kerry in the two months to go before the election, and had appeared at some Democratic Party events.
During his two terms as president, Clinton was an avid jogger also known for his love of fast food. But in January of this year, Clinton said he had cut out junk food after going on "The South Beach Diet" and starting a workout regimen. He has long struggled with a weight problem, but had recently appeared much leaner.
The 6-foot-2 president has remained an active political presence since he left the White House in 2001, whether quietly stopping by his Harlem office or drawing a standing ovation for a rousing speech to Democrats at their July convention in Boston. Most recently, he was on the road plugging his memoirs, "My Life."
Before he was stricken, Clinton had been scheduled to accompany his wife on a two-day tour of upstate New York. Instead, the senator and the couple's daughter, Chelsea, joined Clinton in New York City.
The former first lady made a brief appearance Friday at the New York State Fair in Syracuse, after which she noted that her husband was hospitalized and would need heart surgery. She
Clinton had a cancerous growth removed from his back shortly after leaving office. In 1996, he had a precancerous lesion removed from his nose and a year before that had a benign cyst taken off his chest.
But otherwise, Clinton suffered only the usual problems that often accompany normal aging and a taste for junk food — periods of slightly elevated cholesterol and hearing loss. In 1997, he was fitted with hearing aids, and he also battled allergies.
Clinton first went to a hospital Thursday after suffering the chest pains and shortness of breath, his office said a statement. He spent the night at his Chappaqua home.
"We talked through the day and he said he felt fine and not to worry," said Sen. Clinton.
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.
Pucillo said the blockage was significant enough to warrant an operation.
After the angiogram, "He stopped and looked and me, put out his hand and said, 'Thank you, God bless you,"' said Donna Florio-Bronen, a nurse at the hospital. "He looked great."
In Little Rock, Ark., Clinton's mother-in-law, Dorothy Rodham, said Friday that Clinton had called her with news of his chest pains. "He sounded wonderful as usual and very upbeat as he always is," she said. "I just told him how much I love him."
Clinton also called his stepfather, Dick Kelley, at his Hot Springs, Ark., home, Kelley said. "He's very gung-ho and optimistic about what's going to happen," Kelley said.
Best wishes came in from Kerry and President Bush.
"He's going to be fine," Kerry said at a rally in Newark, Ohio. "But every single one of us wants to extend to him our best wishes, our prayers and our thoughts and I want you all to let a cheer out and clap that he can hear all the way to New York."
Bush, at a campaign stop in West Allis, Wis., sent along "best wishes for a swift and speedy recovery."
Good wishes also came from Harlem.
"I'm going to go home, and I'm going to get my Bible, and there's something I'm going to read for him," said Fred Johnson, a retiree who lives near Clinton's office.