City of the Elves

This was a heart that was transparent like crystal. Every vein was clearly visible. It was almost as if it was actually alive

This "heart" was beating when Abel was looking at it. This scared him. He never thought that this heart was alive. What kind of animal's heart was transparent? And how was it still beating after leaving the body?

Abel observed for a while. The heart was, indeed, alive. It was beating at a rate of once a minute.

This heart was probably Abel's biggest discovery. That's what he thought so, anyway.

 After using his power of the will to scan it, he decided to throw it in the Horadric Cube. A text then popped up, stating that it was a dark gold item called the "immortal heart." 

"Immortal heart." That was the only information provided by the Horadric Cube. It didn't explain what it could, because that's something Abel had to find out himself.