Was running Archer point defense yesterday and had one drop in an ordinary chest. Nothing special, just a standard elite run with no jewel running.
As I've never seen such a drop before in my prior lives, it's pretty uncommon. I know that such a heart can be used to do things like remove the initial level on an iconic (to make for instance a sun elf wizard without a cleric level). What's one worth in terms of trade (thinking mostly in terms of tomes)?