Heatran is one of the hardest pokemon to catch. I found a great way. First save, then talk to it. Hold l and r when the screen starts getting blurry if you want it to be a boy, don't if you want a girl (I don't garrintee that it will be a boy if you hold l and r, it will increase your chances though). Then hit it with some water type moves. When it's hp is about half, start using regularly effective moves (optional). A little later start using grass type moves. when it's hp is really low, come in with false swipe. Then deploy the ultra ball or timer ball and bag it. This may be a little hard, but keep at it.