The keys to a bowel movement without significant straining are stool consistency and proper muscular control. Stool should be unformed, roughly the consistency of pudding. It's usually straightforward to get to that point by avoiding bowel slowers, adding the right amount of fiber supplementation, and drinking plenty of water. Muscular control comes naturally for some, but for others it must be learned. One simple thing that I've found helpful is to try to pee without pooping most of the time (or just pee first if both are needed). By isolating the pooping muscles and increasing awareness of them I'm most of the way toward finer control of them, including the ability to relax them at will.
I hope your heart rate gets under good control. I'm not sure that's from straining at stool, but both things are best managed carefully.