Briar Hearts (and the Briarhearts) are really interesting, in my opinion, but from what I can tell by looking at the UESP, nobody is really sure what the Hearts are or how they work? Just that the hagravens use them as part of their ritual and it essentially makes the person stronger.

I originally thought they were just some sort of plant, or part of a plant, because of their name "briar", them looking like a flower, and they sort of remind me of Spriggans too.

But after looking at it a little further, I was wondering if there's maybe more to them that I'm missing? Are they just part of some rare, "magical" plant, or maybe something created by hagraven sorcery, or. I don't know, something else entirely, maybe from the gods that the Forsworn and hagravens worship?

I'm honestly not up on my TES lore, so if anything above is incorrect and flat out stupid please forgive. And if anyone has any cool theories about where the Hearts might come from and where/how they get the power to essentially revive a dead (or semi-dead, depends how you look at it, I guess) person, I'd love to hear them because I find them pretty cool and interesting

My guess would be that it has something to do with their "Gods of Old". Maybe it's meant to be some kind of like-divine heart given to the Strongest of the Forsworn warriors to improve their strength. It could also very well be some sick old tradition that does nothing more then solidify their position. Knowing the Forsworn it's probably mad up of pieces of many other hearts.. I haven't looked into Briar Hearts so I'm just spit-balling here.

I just love pickpocketing Briar heart.
Best item to pickpocket...