Stop argument ringing sweetheart (5)
I believe the answer is:
cease
'stop' is the definition.
(I know that stop can be written as cease)
'argument ringing sweetheart' is the wordplay.
'argument' becomes 'case' (as in making one's case).
'ringing' is an insertion indicator.
'sweetheart' becomes 'e' (the middle letter or heart of 'sweet').
'case' placed around 'e' is 'CEASE'.
(Other definitions for cease that I've seen before include "Come to an end" , "Culminate" , "Stop, give over" , "Finish, end" , "Discontinue" .)