I asked "then how on earth am I not in serious trouble"? The cardiologist said "fortunately, you seem to have a lot of redundancy here. That one there is blocked, but this other one over here is still able to supply that area."
Diet and exercise are not likely to ever open those up; it's a case of trying to keep it from getting worse. I may have had a mild heart attack with few lingering symptoms, but I still have a time bomb in my chest.