Listen to trumpet initially, and organ (5)
I believe the answer is:
heart
'organ' is the definition.
(the heart is an organ of the body)
'listen to trumpet initially' is the wordplay.
'listen to' becomes 'hear' (to hear something is to listen to it).
'initially' indicates taking the first letters.
The first letter of 'trumpet' is 't'.
'hear'+'t'='HEART'
'and' is the link.
(Other definitions for heart that I've seen before include "Not a club" , "Feeling" , "Playing card - pity" , "Red card" , "Centre; valour" .)