“You are filled with Determination” - Undertale
It has the figure of a red heart, it has a spawn time every 10 minutes approx. It has a spawn rate of 1/200. It plays "I'm Stronger Than You" sung by Chara when spawned. It is the rarest soul you can find in the game. This is one of the seven required souls to obtain the Mystery Mask.
There is also a different name for Heart and it's called Determination