One possibility is that David is looking for his own heart. This explains why he was wandering about the woods, going into strange states claiming “I’m looking.” It also explains why when he first came out of the coma, he went to the toll bridge (where his and Snow’s love was born) looking for his heart. Mary Margaret’s fingerprints are on the heart box because she possesses it completely. Regina could have easily have removed the heart from David, who was in a comma for 28 years in the SB hospital.
[adrotate group="5"]
"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy