Heartfelt but right! (4)
I believe the answer is:
true
This clue is a double definition.
'heartfelt' is the first definition.
(thesaurus)
'right' is the second definition.
(associated in meaning)
'but' is the link.
(Other definitions for true that I've seen before include "Exact, factual" , "Honest and straight" , "Dependable -- loyal" , "Loyal; authentic" , "Agreeing with fact or reality" .)