Mod Item?: Heart of [Spoiler] @ bottom of W Keep

So, finishing up my 1st run through of Throne of Bhaal with a slew of new Mods, after I sent Demogorgon packing he dtopped his heart (labeled Demogorgons Heart, looks like and has item descrip of generic demon heart) and I'm 99% sure this is a mod item... but I can't tell which one it goes to or what to do with it.

Anyone familiar with this thing?