Ancient Petrified Heart can be placed on a Ancient Altar and sacrificed to summon The Dark Guardian boss. The player must have the Ancient Ceremonial Dagger equipped.
The Ancient Petrified Heart is only obtainable by killing and looting an Ancient Guardian and can not be bought from a Merchant.
Trivia
- The Ancient Petrified Heart and Ancient Ceremonial Dagger can only be found by killing and looting an Ancient Guardian. It is possible to receive both items off of 1 Ancient Guardian.