She otherwise captures his heart (5)
I believe the answer is:
elsie
'she' is the definition.
'otherwise captures his heart' is the wordplay.
'otherwise' becomes 'else' (synonyms).
'captures' indicates putting letters inside.
'heart' indicates the central letters.
The central letter of 'his' is 'i'.
'else' going around 'i' is 'ELSIE'.
(Other definitions for elsie that I've seen before include "Lady" , "woman" , "Name for girl" , "Female name; rhymes with London football team" , "Girl's name" .)