'Heat' is another term to describe thermal energy, whether the thermal energy just sits in some object or substance, or flows from one object to another one that's cooler.
'Heat' is NOT another word for 'Temperature'. If you think of it that way, then you'll have a hard time UNlearning that idea and getting yourself unmuddled and straightened out. Please don't even go there.
This is a centripetal force problem where tension supplies the centripetal force needed to keep the stone moving in a circular manner. That formula for that is
and filling in what we know:
and solve that for v:
which gives us a velocity of .07 m/s. Anything greater than this will break the string.
