Middle card (5)
I believe the answer is:
heart
This clue is a double definition.
'middle' is the first definition.
('heart' can be a synonym of 'middle')
'card' is the second definition.
(heart is a kind of card)
(Other definitions for heart that I've seen before include "Middle" , "Blood-pumping organ" , "Centre; core" , "Spirit - core" , "Player for Scottish team" .)