Heart perhaps shown by referee (3,4)
I believe the answer is:
red card
I believe this is a double definition.
'heart perhaps' is the first definition.
(hearts are red in a deck of cards)
'shown by referee' is the second definition.
(a referee might show a red card)
(Other definitions for red card that I've seen before include "used to send offenders packing" , "Sending-off signal?" , "It's shown for a serious infringement of the rules" , "What ref shows to player being sent off" , "Referee's sanction" .)