When I have a good hand in poker why does my heart rate go up and my vein pulsate?

Chris - Well, this is your sympathetic nervous system. We have two arms to our autonomic nervous system. The thing that controls our unconscious bodily systems. We have the sympathetic nervous system, which you activate when you need to fight or when you undergo flight, you wanna run away, and you have the parasympathetic nervous system when you rest and digest things. When you get excited, your sympathetic nervous system turns on. This makes your pupils big, it makes your heart rate go up., your blood pressure goes up, you start sweating. You also might get slightly trembly and as a result you give yourself away because you're obviously getting excited. So, trained people know how to slightly damp down that reflex so that they don't actually display those innermost feelings. So, it's a question actually of probably self control and training yourself not to get too excited.