Clinton blames himself -- a bad diet, a busy work schedule and ignoring warning signs -- for his health ordeal.
"Since I left the White House, maybe if I had stayed on a lower fat diet. Maybe if I had … not eaten so many hamburgers and steaks, which I love, maybe if I had, you know, had slightly less stress in my life … maybe it would have been different," he said.
In his first interview since his surgery, Clinton said his wife, Sen. Hillary Rodham Clinton, was not worried that he was returning to political activities too early, but she didn't want him to do too much, either. When he was first released from the hospital, she made sure that he didn't field too many phone calls.
"She was afraid I'd be on the phone too quick when I came home. And so we rerouted our phones to the office," Clinton said. "And it was interesting. We got 100,000 e-mails, 10,000 letters, and hundreds and hundreds of calls. And they organized the phone calls for me, and I'm answering them a little along as I can."
Still, Clinton does not think he is taking a risk by hitting the campaign trail for Kerry so soon after surgery. The race between Bush and Kerry is too close to call, Clinton said, and the consequences are monumental.
"I want to do this," Clinton said. "Senator Kerry asked me to do it, and I want to do it. And … because it's [the race for the White House] close and because I think it's important. And because the differences between the two candidates and the courses they'll pursue in the next four years are so profound."
The rest of Diane Sawyer's interview with Clinton will air Thursday on "Primetime Live."