Play heroine part and heartless Iago amazingly (6)
I believe the answer is:
portia
'play heroine' is the definition.
(heroine of Shakespeare's The Merchant of Venice)
'part and heartless iago amazingly' is the wordplay.
'and' is a charade indicator (letters next to each other).
'heartless' says to hollow out the word (remove centre letters).
'amazingly' is an anagram indicator.
'iago' with its centre taken out is 'io'.
'part'+'io'='partio'
'partio' with letters rearranged gives 'PORTIA'.
(Other definitions for portia that I've seen before include "Shakespearian legal eagle" , "judge" , "Character in "Julius Caesar" or "The Merchant of Venice"" , "Advocate of cross-dressing" , "Merchant of Venice girl" .)