What to do if i want to know what happens when you exercise over your target heart rate zone?

Nothing: When people ask me about what their target hr should be when working out, i tell them that the workout intensity is more important than heart rate. So if you feel like you are overdoing it, are exhausted and feeling sick after your workout, and your hr was less than target, it was too much. Decrease intensity. If hr is higher than target, and you feel ok afterwards, that's ok, no problem.