A relation, not being heartless, makes a gift (6)
I believe the answer is:
talent
'a gift' is the definition.
(I know that gift can be written as talent)
'a relation not being heartless' is the wordplay.
'a relation' becomes 'tale' (I've seen this before).
'being heartless' means to remove the middle letters.
'not' with its middle removed is 'nt'.
'tale'+'nt'='TALENT'
'makes' acts as a link.
(Other definitions for talent that I've seen before include "Natural ability or flair" , "Innate ability, flair" , "some scouts are looking for" , "Dull means claw" , "Natural ability or quality" .)