male cat hissing at female

Question
We just had our female spayed two days ago, our male cat keeps hissing at her if she gets too close to him.  He is neutered and they have lived with us for almost two years. We got them at the same time, they're the same age and have always gotten along.  We're very concerned about why he's doing this.

Answer
well she now smells all medicinal...because of the surgery and the stuff they used to clean the area where her stitches are. plus she probably feels really crappy right now. just give it time. if she has stitches that will be removed later, they will most likely be back to normal by then.