Unless the guy is more than 10 ft away, and has no gun, you are going to be LUCKY, to get more than 50% hits on his chest,, and many of those chest hits may well be without immediate effect, if shock doesnt become an issue, because he can continue to operate just FINE for over 5 secs with his heart blown apart. Enough have done so after 12 ga hits for us to know this. One lung being hit means nothing, until he drowns in his own blood, which could take MINUTES. liver or spleen hit, or blood vessel hit can take MANY seconds to bleed him out, while he is shooting or stabbing you at the rate of 4x per sec. So GOOD hits mostlycome from LOTS of shots being fired, by skilled shottists, using low recoil loads, easily controled guns. Trouble, is, sometimes even good hits dont stop the guy. If you can hit the 4" heart, you can also hit the 4" brain, so why not go with what is a LOT more likely to have the instant result needed (if you TRULY think that you can hit the heart, that is.)