I googled "aztec sacrifice," "aztec sacrifice heart removal," "corpse heart removed," "heart removal live victim," "heart removal corpse," and various permutations thereof. I also tried to read some articles on how the heart works but I didn't understand a word of it, and I searched through the tags and such for this community.
Thanks, hope I'm not being stupid! Advice on doing better searches would also be appreciated because apparently I fail, epically.