Skills in heart surgery (4)
I believe the answer is:
arts
'skills' is the definition.
(I've seen this before)
'in heart surgery' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ARTS' is hidden within 'heart surgery'.
(Other definitions for arts that I've seen before include "Creative activities such as painting and music." , "they may be performing" , "___ and crafts" , "Aesthetic pursuits or creations" , "Wiles, skills" .)