Here's a nice display of the vitals and arteries of a Whitetail deer. I used to always try for the heart, but have become convinced a shot passing through the central core of the lungs anchors the deer faster. Think three dinemsional whenever you aim at the deer. The bullet will strike the surface, but where will a straight path take it? A trick in bowhunting is to aim for where you want the arrow to EXIT the body. Makes you think about internal structures. I have had deer with shredded hearts still put 200 yards behind them. Blasting both lungs gives the same effect as when you take a shot to the solar plexus. Something this drawing doesn't show is the 'elbow' just at the lower extreme of the heart in this pose. Asking a round ball to blow throuh that and then continue unerringly straight on into the heart is asking a lot, especially in the marginal calibers.
One of my pet peeves is in 3-D archery events where the McKenzie deer targets (with outlined scoring rings) are used. An angled shot that would score 10X on the target would, in reality, chatter the broadhead along the deers ribs and probably result in a wound far behind where the "Super-Kill Dot" indicates.
I apologize if I drag traditional archery into most of my hunting comments. I treat my muzzleloaders like very easy to draw bows with 4X the range and hunt accordingly.