The Heart of Mantorok (full name: Black Heart of Mantorok) is one of the "Corpse God's" hearts. It is his "essence" and holds the last vestiges of his power since he was impaled with the enchanted stakes. In the game the other Ancients warn Pious about the power of the Heart when instructing him to find it. They seem to almost fear the power of the heart when speaking about it. Nonetheless, they dismissed Pious's concerns when he attempted to warn them about a possible miscalculation in their plan to obliterate Mantorok relating to the heart shortly before attending to their plan to kill Charlemagne the Frank.
The Keeper of the Heart remains nameless and his origin is unknown. However, what is known is that he gives it to Ellia. Ellia gives it to Dr. Lindsey. Lindsey gives it to Edward Roivas, and is finally found by Alex behind one of Lindsey's pulp fiction books in the library, who uses it to help summon her Ancient at the end of the game.