Pasternak's hard heart! (5)
I believe the answer is:
stern
'hard heart' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'pasternak's' is the wordplay.
'STERN' is hidden in amongst the letters.
However, I'm uncertain how this is indicated.
Can you help me to learn more?
(Other definitions for stern that I've seen before include "Severe, demanding" , "Severe; grimly serious" , "Harsh at the back of the ship" , "Severe part of the ship?" , "Looking severe" .)