Having few worries about a heartless whistle-blower (8)
I believe the answer is:
carefree
'having few worries' is the definition.
(without a care in the world)
'about a heartless whistle-blower' is the wordplay.
'about' becomes 'ca' (abbreviation for 'circa').
'a heartless' means to remove the middle letters.
'whistle blower' becomes 'referee' (I've seen this in another clue).
'referee' with its centre removed is 'refree'.
'ca'+'refree'='CAREFREE'
(Other definitions for carefree that I've seen before include "Unconcerned - cheerful" , "Without worry or responsibility" , "Jaunty" , "Untroubled" , "Endures" .)