Would you be kind enough to give me your considered opinion concerning the interpretation of the expressions in bold in the following sentences?
I didn’t know him well, but I felt that at heart he as decent, sound and healthy.
With his white head and his loneliness he had remained young and green at heart.
The shop looked like a jeweler’s shop…Only the conventional sigh over a side-entrance showed that at heart of hearts it as a pawnbroker’s. (A. Bennett, “The Old Wives Tales”)
My father was for all his talk at heart a man of silence. (J. Updike, “The Centaur”)
at heart = in heart = in one’s heart = in one’s heart of hearts = fundamentally, basically, deep in oneself