On Once Upon a Time, hearts are central to many kinds of magic. Rip out someone's heart and you can control them. Put someone's heart in stasis and you can preserve them. The heart of the thing one loves most is a necessary ingredient for the Dark Curse.
It seems to be implied that if one is the product of true love, one's heart cannot be ripped out.
Mr. Gold: I created the curse, dearie, but I didn’t make you. I merely took advantage of what you are – the product of true love. That’s why you’re powerful. And everything you’ve done, you’ve done yourself.
Emma: So you don’t know.
Mr. Gold: Know what?
Emma: Cora… Tried to rip my heart out, but she couldn’t. She was blasted back by something inside me. By… By-
Mr. Gold: By magic. Whatever that was, I didn’t do that. You did.
—Season 2, Episode 9 : Queen of Hearts
How, then, were Regina and Hades able to remove Emma's heart in Season 5, Episode 20?