Heard about organ (3)
I believe the answer is:
ear
'organ' is the definition.
(the ear is an organ)
'heard about' is the wordplay.
'about' says the answer is hidden in the clue (the clue goes around or about the answer).
'EAR' can be found hidden inside 'heard'.
(Other definitions for ear that I've seen before include "Spike (wheat)" , "Seed container" , "Musical ability" , "A corny bit" , "Head of, eg, corn" .)