Given by Vidyadhar, an outer plane creature you encounter during Zaviak's Vision Quest in Chapter 10, after you successfully answer his riddle ("Bees"), or by simply killing him.
In-game description Edit
|“||Modrons are mechanical creatures of utter law and efficiency that make their home on Mechanus. Many think of modrons as soulless, emotionless beings without a heart to speak of, but this item proves those beliefs false. The Modron Heart is a core of pure law that strengthens its wearer in battle against chaotic creatures.||”|