About fifteen years ago I read a book summarizing research into the effects of different types and calibers of handguns and handgun ammunition. (Long story short: Clinton was trying to ban semiautomatic handguns or something, so my dad developed a sudden interest in buying a gun, and he borrowed some books from a friend who was quite an enthusiast.) The study was a survey of thousands of police reports on shootings,…
Here's a PDF analyzing the effectiveness of firearms. It was written in 1989 so it is a bit out of date. Perhaps someone with more experience with firearms can check to see if the article is still relevant.
It does confirm that "Even if the heart is instantly destroyed, there is sufficient oxygen in the brain to support full and complete voluntary action for 10-15 seconds".