I wouldn't call my self one of today's enlightened by a long stretch. But I've been putting a lot of work into working with my heart beat and heart rate. I spent months working on my prone hold and technique, and got to a point where now my heart beat is the most noticeable 'wobble'.
Haven't found the best solution for me just yet, but still working on it. My current plan is to up my fitness and lower my resting heart rate. I keep meaning to start a logbook of some kind to track my progress. Weapon of choice is a Concept 2 rowing machine we got off the bay. This is definitely not a quick fix but enjoying it so far.
I would be interested to hear what heart beat methods you springer shooters had back then?