The Heart of Nanda Parbat was a mystical orb.
All the monks of Nanda Parbat were connected to the Heart. Once it was removed, the essence of the monks was absorbed into the orb, making them all comatose. Grodd sent several Legion of Doom members to retrieve it so he could use it as a power source for his transformation machine.
The plan was foiled and the heart restored to its original place, and all the monks awoke.