The Witcher 2: Assassins of Kings[]
Gargoyle heart can be used to craft elemental stone, but given that it is significantly more expensive, this seems a poor use of the ingredient.
The Witcher 3: Wild Hunt[]
Gargoyle heart is an alchemy ingredient. It is not needed to craft anything but can be dismantled into monster heart and powdered monster tissue.
It is a random drop from all gargoyles.