From Formspring: Does that mean that a multiheaded dragon (if there are any) would have one brain in its torso or something?

No. One of the heads would be dominant, but the multi-headed dragon could switch between them at will. So, to kill it, you'd have to either hit the heart or destroy all the heads. I know it doesn't really make sense. All I can say to that is: they're dragons.

Dragons.