Nurses stress badly about strikes at heart (7)
I believe the answer is:
sisters
'nurses' is the definition.
(female nurses are often addressed as sister)
'stress badly about strikes at heart' is the wordplay.
'badly' indicates anagramming the letters (letters in the wrong order).
'about' is an insertion indicator.
'at heart' says to take the centre.
The centre of 'strikes' is 'i'.
'stress' is an anagram of 'ssters'.
'ssters' enclosing 'i' is 'SISTERS'.
(Other definitions for sisters that I've seen before include "Nuns - nurses - siblings" , "Members of the family" , "Female siblings" , "Resists for relatives" , "Patient attention required from such" .)