The perfect shot angle for me is a deer quartering slightly away, and place the arrow right in the pocket behind the shoulder to go for the heart shot. If you cut anything in the heart area (heart, veins, artery), they will bleed out much faster than a lung shot, travel a shorter distance, and leave a trail easier to find. If the shot is longer and/or the deer is broadside, or slightly quartering to me, then I'll generally get a more lung shot. It will also work, but they run a little further, and a blood trail can be a little harder to follow sometimes. But s good shot in the vitals will do the job.