Why is grapefruit not allowed with Lipitor?

I have been taking Lipitor with three heart stents for the past ten years. After all this time, i just noticed a one-liner on the packaging that states: avoid grapefruit, while taking Lipitor. I am not a big grapefruit lover, but i wonder what effect that grapefruit has on Lipitor? Question: If grapefruit has this effect on Lipitor, does it also have the same effect on other heart medications? If so, should we be concerned?