Live, having received new heart! Use lungs! (7)
I believe the answer is:
breathe
'use lungs' is the definition.
(you use your lungs to breathe)
'live having received new heart' is the wordplay.
'live' becomes 'be' (synonyms).
'having received' indicates putting letters inside.
'new' indicates anagramming the letters.
'heart' is an anagram of 'reath'.
'be' placed around 'reath' is 'BREATHE'.
(Other definitions for breathe that I've seen before include "Take air in and out of the lungs" , "Absorb air" , "Inspire and expire air" , "Do this before you go under" , "Take in 30" .)