I've had both a male and a female cat for about two years now. They are both fixed, but all of a sudden my male cat has become overly aggressive with my female cat. He always starts fights with her, and she doesn't fight back. Its getting bad because my girl cat has been hurt. They are both almost three and are not related. Does anyone know what might be causing his aggression?

Has the female been to the vet recently? I read somewhere that if you have taken one cat to the vet, the other cats will smell it and become hostile for as long as the smell lasts.
Or if there is a change in the household, this can also play a dynamic in their relationship like, for example, if you were looking after someone else's cat temporarily?
The male could have been spooked..
Usually tiffs like that are temporary though.. depending on how temper-mental your cats are.

The female cat hasn't been anywhere recently, and nothing has changed in the household. My male cat seems to be hurt too now, but I've heard that cats can "milk" and illness so to speak. Is that true? Thanks for the response

Perhaps it's an affection thing. If he's noticed the girl getting more, he might be feeling a bit left out.