Sarah gives Rosalie heart (3)
I believe the answer is:
sal
'sarah' is the definition.
(Sally is a common pet form of Sarah)
'rosalie heart' is the wordplay.
'heart' means to look at the middle letters.
The middle letters of 'rosalie' are 'SAL'.
'gives' acts as a link.
(Other definitions for sal that I've seen before include "girl?" , "- - volatile" , "Sarah (dim.)" .)