I am starting to question whether I am shooting at the right spot on a deer. The last two bucks I've shot with my bow I've lost. and the sad part is that I thought i hit them good. I let them go several hours before looking but the the blood trail just stopped.

I always aim behind the shoulder right in the middle of the deer but maybe I'm too high or low. Is the heart right in the middle (vertically speaking) of the deer or is it a little lower than center? Also, is the heart right behind the shoulder at broadside (legsat 90 degrees tothe body)or is part of it between the shoulders at this angle? Is there a good diagram or video tutorial on the spot to shoot a deer?