Speaking on CBS's The Early Show, the Super Bowl winner explained that he discovered he had two blocked arteries during his second attempt to land a place among the castaways.
"I tried to get on it about six or seven years ago, did all my applications and my video but they turned me down," he said.
"I tried again about three years ago and went through the whole process and thought I'd get on - they pretty well accepted me. I went through the medical and the Survivor doctor called me and said, 'Coach, we'd love to have you but you have two blocked arteries. One is 70% blocked, one is 100% blocked. You better see your cardiologist.'"
He went on to say that he took the doctor's advice and also adopted a "strict work-out routine" which saw his cholesterol drop. He added that he decided to try out for the show again once he was healthy.
"Finally got on this time!" he laughed. "In fact, Survivor may have helped me survive."
Johnson - who previously said that he shared football stories to boost his teammates' morale - also discussed his audition tapes in a separate interview with TV Squad, saying: "One video, I was out on the beach and talking about how I can outwit and outlast. In another video I talked about how I've won a couple of national championships and a couple of Super Bowls and what better way to end a career than to win Survivor?"
Survivor: Nicaragua premieres tomorrow night at 8/7c on CBS.
> 'Survivor: Nicaragua': Meet Jimmy Johnson