The Frozen Heart of Isuldof is an item looted from the grave of Isuldof Iceheart at Shield Hill. Isuldof's ghost now haunts the area, seeking revenge and calling curses upon the thieves (and pretty much everyone else around).
"Mad" Jonah Sterling took the heart from the grave, and it drove him mad. He retreated to a cave north of Scalawag Point and barred (well, 'beared') himself in. Eventually, he tossed the heart into the den with Hozzer, but has not recovered his sanity.
Objective of Edit
The heart can be found in the bear den[32.4, 78.7], and is an objective of  .