I've never shot for the heart; never made sense to me; why crowd the shoulder and risk lack of penetration? Ultimately, hypoxia/anoxia puts your deer down. Quickest way to do that is a bilateral pneumo/hemothorax, preferably a passthrough. It really doesn't take that much to get full penetration on deer; I've used trad tackle from 65 to 48 lbs and heavy, 11-12 grains/lb arrows, usually tapered cedar, and always with 2 blade COC broadheads, mainly because they are the easiest for me to get sharp. Deer ribs offer little resistance to arrows; lungs even less. Probably why, in my first season of saddlehunting, I'm setting up pretty low...8-12 feet. Don't like the shot angle when I get higher. That may change if I keep getting busted, but after decades of groundhunting, habits are hard to break.