Science

This reminds me of some experimental forensic archeology, though I didn't have a source to quote. So if nothing else it makes a good story.

Curious to see if it was even physically possible for Aztecs tob sacrifice as many human hearts as documented by conquistadors, a researcher decided to practice on human analogues. Using a small replica sacrificial knife, they were able to determine that a single incision in the abdomen, above the stomach but below the ribs, made for easy access to the chest. Using one hand that also had a blade in it, they could never the arteries and extract the heart. After a little practice and a bit of math, they figured that a skilled and practiced priest could extract about 5 or 6 hearts a minute - practically as fast as the victims could be presented and cruise corpsed removed.

So if true, them it's been scientifically proven that the fastest way to a man's heart is not through his stomach, but rather a little above it and up under the ribcage.