Not opening father's new suit (6)
I believe the answer is:
'suit' is the definition.
(I've seen this before)
'not opening father's new' is the wordplay.
'not opening' means to remove the first letter (the opening letter is removed).
'new' indicates an anagram.
'fathers' with its first letter taken off is 'athers'.
'athers' is an anagram of 'HEARTS'.
(Other definitions for hearts that I've seen before include "Red playing cards" , "Cores" , "Suit in pack" , "Card suit and essential organs" , "Card game and centres of emotions, it's said" .)