Sedated, somehow getting his heart fixed (8)
I believe the answer is:
steadied
'fixed' is the definition.
'sedated somehow getting his heart' is the wordplay.
'somehow' indicates an anagram.
'getting' is an insertion indicator.
'heart' indicates the central letters.
The middle of 'his' is 'i'.
'sedated' with letters rearranged gives 'steaded'.
'steaded' going around 'i' is 'STEADIED'.
(Other definitions for steadied that I've seen before include "Supported, controlled" , "calmed down" , "made stable" , "Braced" , "Made firm and balanced" .)