Beowulf question

I read a book my father gave me in the early 80's about a man who goes to an Incan/Aztec culture but something is wrong and he can't figure it out. Turns out that they are still sacrificing humans. The book ends with him on the altar having his heart torn out...

Does anyone know what the title of this book is?

It's not Beowulf, it just wouldn't let me post if the context was blank...