Well heretics is a vague term; it applies to anyone that doesn't confer with your own ideals. A good example of heretic was Joan of Arc just because she dressed as a man to join the army. Because of this she was labeled a heretic and burned at the stake.

Heretics are defined as people who deny an essential truth about the teachings of the church. Besides, Joan of Arc's was a politically motivated case, not a religious one.
http://en.wikipedia.org/wiki/Joan_of_arc#Trial

Yes but the original court case labeled her as a heretic because she said she dressed as a male. It wasn't until another court case revoked her as not a heretic.