My heart listened to (3)
I believe the answer is:
cor
'my' is the definition.
(both are expressions of surprise)
'heart listened to' is the wordplay.
'heart' becomes 'core' (synonyms).
'listened to' indicates a 'sounds like' (homophone) clue.
'core' is a homophone of 'COR'.
(Other definitions for cor that I've seen before include "Expression of surprise" , "Surprised expression" , "Blimey" , "Gosh" .)