No need to worry. All the vital organs are protected by the body during a fast, including the heart and brain.
The body is selective, and will always eat non essential stuff first, and that includes growths etc, which is good news for us.
That is why the waterfast is so beneficial, all the bad stuff, damaged cells, scar tissue etc gets consumed. Toxins are released and expelled. The body has a chance to do deep healing because it hasn't got to digest food. The body comes back into balance.