Loving but discovered to have no heart (4)
I believe the answer is:
fond
'loving' is the definition.
(similar in meaning)
'discovered to have no heart' is the wordplay.
'discovered' becomes 'found' (to discover is to find).
'to have no heart' means to remove the middle letters (I've seen 'has no heart' mean this).
'found' with its middle taken out is 'FOND'.
'but' acts as a link.
(Other definitions for fond that I've seen before include "Partial to" , "Feeling affection, maybe foolish" , "Affectionate, maybe foolish" , "Affectionate - tender" , "Keen on; indulgent" .)