Deliver fresh heart ahead of signal to act (6)
I believe the answer is:
rescue
'deliver' is the definition.
(synonyms)
'fresh heart ahead of signal to act' is the wordplay.
'heart' means to look at the middle letters.
'ahead of' says to put letters next to each other (some letters go in front of others).
'signal to act' becomes 'cue' (an actor's cue).
The central letters of 'fresh' are 'res'.
'res'+'cue'='RESCUE'
(Other definitions for rescue that I've seen before include "Extricate" , "liberation" , "Save someone from a dangerous situation" , "Salvage" , "Secure (anag) - deliverance" .)