The rules of a heads up poker game are similar to that of any other poker game.
What can you do when you've just lost a big hand, and now you are close to getting knocked out of your heads up match?
One of the first things you can do is calm down. Nothing is worse than getting sucked out on or bad beat in a high dollar no limit heads up game, believe me I know. The last thing you want to do is lose your cool. If your opponent is talking trash and it's getting under your skin, turn off the chat. Many poker rooms have a feature that allows you to turn off the chat.
The situation we are trying to avoid is the one which involves going all in with a garbage hand, and after losing that hand, buying into a $100 heads up because you are pissed off. This is the beginning of tilt and can ultimately lead to losing a huge chunk, if not all of your bankroll.
The only thing that can really keep you from getting on tilt is to check your ego. This is a hard thing to do because most of us have large egos, which is why we are poker players.