I certainly don't think that emotional expression has anything to do with the distinction of heart of flesh/heart of stone I'm trying to pin down here; in fact I would say vehemently that it absolutely doesn't. For example, take Jane Austen's Sense and Sensibility, a book I've discussed in this LiveJournal before. Marianne and Elinor, two sisters each in love, both have "hearts of flesh" but whereas Marianne prides herself in allowing full rein to her emotion, both positive and negative, even to the point where she eventually endangers her life, Elinor, who has deep reserve, does not, not wanting to inflict her emotions on her family. Yet, as she tells Marianne eventually, "just because you can't see it doesn't mean I don't feel it. I do."

Conversely, the character who clearly has a heart of stone, Willoughby, acts as Marianne, always allowing free expression to his unchecked emotion. Because of his essential selfishness, however, he eventually abandons Marianne because she is not rich enough. Col. Brandon, ridiculed by Marianne for his dull, reserved demeanor, is eventually revealed to have suffered the greatest heartbreak of all, but he always hid it.