Try ties on the outside for suit (6)
I believe the answer is:
'for suit' is the definition.
(hearts is a playing card suit)
'try ties on the outside' is the wordplay.
'try' becomes 'hear' (as in to try someone in court or hear their case).
'on the outside' says to hollow out the word (remove centre letters).
'ties' with its centre removed is 'ts'.
(Other definitions for hearts that I've seen before include "Central parts" , "Edinburgh football team - suit" , "Scots club nickname; suit" , "Red playing cards" , "Playing card suit" .)