How do I calm down from anger?

For the last week my wife has changed and become very hostile and rude. I can understand all the things that can cause her to do this. What I want to know is when she hits below the belt and I get furious, how do I calm down? Breathing doesn't work. I just want to retaliate. I of course don't want to make it worse, so what can I do to calm down? I am not talking about being in a bad mood, but anger and rage.