Alright, to all of you, I would like to concede this point, not because my viewpoint has changed, but because my original post was overexaggerated, due to rage resulting from an issue in my life that I'm not sure if I have permission to tell you, (which I shouldn't be taking out on you guys anyway) and extremely heavy bias.
Now, filtering out the bias and exaggeration, I'll try to make a more universal essay regarding shot placement:
First, I would like to say that headhsots are just as effective as heartshots in a situation where you cannot possibly miss, (read: contact shot) they are less effective in every other circumstance because if you're a centimetre off when shooting the heart, your shots hit the aorta, or at least a lung. If you're a centimetre off when shooting the brain, you hit... air. No matter how good at it you are or what weapon you are using, you can't miss well enough to win a firefight.
Further, if you shoot the heart the brain dies immediately, if you shoot the brain the heart keeps beating for a while. I understand this is completely irrelevent in a firefight, but the point still stands.
As for what happens when you miss the main target:
If you miss the heart, around it are the aorta, spinal coloumn and lungs. Around the brain is the face, the skull and air.
If you hit the aorta, the target hits the ground in a second, is unconscious in less than ten and dead in 30.
If you hit the face, you disfigure the target, cause bleeding, and may or may not kill, depending on the part of the face hit and the weapon used. In any case, it will not be a swift death, and will be extremely painful.
If you hit the spinal coloumn, you may paralyze the target, but modern medical attention will be more than enough to ensure their survival. This kind of shot, as it is generally non-lethal but leaves the target crippled for life, is against my morals, but is generally accidental.
If you hit the skull, you may or may not cause spalling inside it, depending on the bullet's power, angle, age of target and the part of the skull hit. As it is unreliable in causing death, but generally disfigures the target and frequently cripples them, this shot is also against my morals.
If you hit the lungs, the target looses some of their ability to oxygenate blood immediately, causing swift hypoxia, as well as slowly filling the lungs with blood, causing asphixiation, which results in, you guessed it, further hypoxia.
If you hit the air... it comes back. Once again, you can't miss well enough to win a firefight.
Finally, as far as lethality of the shots... the brain is, strictly speaking, less lethal than the heart, but it doesn't matter because all but the msot underpowered of weapons will simply do so much damage that the target will be dead instantaneously anyway, if not because of the hole in the head (which are frequently survived, for a good example see: http://www.metro.co.uk/news/828580-drummer-survives-impaling-head-on-railings
) than because of the shockwave caused by the bullet's passing (which is essentially blunt force, but I digress) but this is beside the point. A bullet through the heart will kill them equally dead, with slightly greater reliability and an underpowered hit will never leave them cruelly crippled for life. (Which is considered a-moral in my mind.)
Looking in these contexts, it's easy to understand why I do not subscribe to headshots.