I have posted this numerous times but it's been a while so here it is again.

From the perspective of if the deer is going to die it doesn't matter which one you hit or if you hit both. You can't live very long with out either.

DeerandbearhoG is correct in that you can't take out the heart with out taking out the lungs.

Having said that, a double lung shot while leaving the heart in tact will result in the deer passing out from lack of oxygen to the brain quicker than if you had taken out both the heart and lungs.

The reason is that the lungs are filled with millions upon millions of blood vessels. When the lungs are punctured (as with a broadhead), or a major blood vessel is severed, (as in the aorta) there is a massive drop in blood pressure. The brain instantly and involuntarily tells the heart to pump blood faster and faster to make up for this drop in blood pressure. The harder the heart is pumping the quicker the blood is leaving the organs and the body, the faster the brain is deprived of oxygen and the faster the animal passes out. The animal doesn't actually die for a minute or two.

If you take out the heart it can't pump blood. If it isn't pumping then the blood just drains out of the hole you just put in it.

Both are deadly but a double lung will result in a shorter blood trail. All other things being equal.


Oh, and bullets are a completely different issue as they work on shock and massive trauma to internal organs and not massive hemorrhaging.