My dad was an excellent marksman with a long bow. When he taught me to shoot the first thing he did was make me practice slowing my heart down. Once I could do this with my hand feeling my heart and had it down I got to use the bow. It was a breathing pattern, I can't always do it now but It was a full breath, then a short breath, then I would fully exhale, and after a slight pause pull in half a breath and then hold my breath.
My heart would skip a beat, the rythm was interupted and actually seemed to accelerate but there was a definite moment just after I held my breath when my heart would stop.
visually it would look like this:
beat...beat...beat... ! ...beatbeat...beat...beat...
This made it possible for me to shoot between beats, which is especially important when you are right-handed, as you hold the bow with your left. The left arm being closest to the heart of course. I found I need a 10-15 seconds to recover after this before I could do it again.
I've heard that special forces marksman have some similar techniques for body control. I'd be interested to know how this works.
