The Heart Beast appears in "The Enchiridion!" as one of Finn's many trials given to him by the Dark Magician. He killed it by punching it repeatedly until it exploded (spewing blood in the process). The Dark Magician claims that it is "completely evil."
The heart beast has no face but it has a purple glowing skeleton arm, a scarf, and strongly resembles a human heart.
- This is the first and only character to release profuse amounts of red blood when defeated.
- It, along with Ricardio, are the only anthropomorphic hearts on Adventure Time.