Mephit Heart is a common misc item that can be extracted and combined. So far I haven't been able to figure out its utility.
This heart is tiny and jagged. In certain lights, it looks closer to stone than flesh.
Properties
Miscellaneous Items
Single Use
Rarity: Common
Weight: 0.05 kg / 0.1 lb
Price: 2 gp
Effect
Action
Extract to combine with two other unknown elements to create unknown item. 
Where to find
Cellar of the Crimson Draught, Araj Obladra's residence in the Lower City.