Actually, shotguns don't spread-shot nearly as much in reality as they do in movies (in other words, enough to make a giant hole) and, in fact, it's not unheard of for shotgunners to stick a standard 4x zoom ACOG on the things. A shotgun blast to the chest, close-range or otherwise (close range would actually lessen the chance of it hitting the heart, since it hasn't spread as much yet) can still leave someone mortally wounded but alive long enough to keep going on adrenaline, shock and willpower, though it's probably less likely than the same happening with a single pistol or rifle shot.