Heart-throb: ambiguous, captivating lead in film (5)
I believe the answer is:
bambi
'lead in film' is the definition.
(main character in the Disney film Bambi)
'heart-throb ambiguous captivating' is the wordplay.
'heart' says the answer is hidden in the clue (I've seen 'heart of' mean this).
'BAMBI' is hidden within 'throb ambiguous captivating'.
(Other definitions for bambi that I've seen before include "D [Disney] made it" , "7's fawn" , "Walt Disney film with lovable deer" , "Disney character" , "Disney's young deer" .)