as Sluff said, it wouldn't hurt to have the Surgeon who placed the fistula have a look at it. Mine is on the inside of my right arm, above the elbow, and from there up is always "warmer" than the rest of my arm. It could be from the increase of blood from your fistula, that is the heat you are feeling. Hopefully its not an infection in yours. Lets us know how things turn out - good luck