Possibly because she recognized it, or possibly because the threat had her focused on every signal he gave off, Regina didn't miss the pain. The darkness.

Gaze narrowing, she lifted a hand to touch his bare chest. Testing. She didn't sink her fingers in, didn't try to take it out, but she didn't need to to feel that his heart's energy was wrong somehow. She pursed her lips in consternation, thrown out of her panic by the possibility that they were the same somehow.

"For me too." Her heart might be there in her chest, but it was a yawning abyss of grief and loss where the only light was Snow.