Heart to heart organ (3)
I believe the answer is:
ear
'organ' is the definition.
(the ear is an organ)
'heart to heart' is the wordplay.
'heart' means to look at the middle letters.
The middle of 'heart' is 'EAR'.
(Other definitions for ear that I've seen before include "Spike (wheat)" , "good sense of music" , "willingness to listen" , "Van Gogh missing body part" , "Place for a plug" .)