I doubt that heart actually has anything to do with Kathryn. Regina just tampered with the test results, (or completely fabricated them if the heart never actually went anywhere to be tested…we don’t know that Storybrooke has a DNA lab and if Regina controls everything that goes in and out of town, she’s not letting that heart go to no DNA lab in Boston).
If it IS actually Kathryn’s heart, I reckon that means she’s dead.
I don’t see how it could be a magically removed heart where the person is still living, because Graham’s “heart” didn’t look like an actual heart. And the heart in the box that Ruby found was quite obviously an actual, flesh and blood heart, considering no one questioned why it looked strange and was glowing red. So I think Regina just dug one of her trophy hearts out of her collection and stuffed it in the box.