Playwright’s maxim about hearts (4)
I believe the answer is:
shaw
'playwright's' is the definition.
(George Bernard Shaw)
'maxim about hearts' is the wordplay.
'maxim' becomes 'saw' (I've seen this in another clue).
'about' indicates putting letters inside.
'hearts' becomes 'h' (abbreviation used in card games e.g. bridge).
'saw' placed around 'h' is 'SHAW'.
(Other definitions for shaw that I've seen before include "Man and Superman playwright" , "Irish playwright, d. 1950" , "Irish author" , "making an appearance in Craiglockhart?" , "G. B. ---; T. E. ---" .)