Very big balls? Heaven-sent part of the body! (5)
I believe the answer is:
torso
'the body' is the definition.
(a person's middle)
'very big balls? heaven-sent part of' is the wordplay.
'very big balls? heaven' becomes 'tor' (I can't justify this - if you can you should believe this answer much more).
'part' indicates taking the first letters.
'of' becomes 'o''.
The first letter of 'sent' is 's'.
'tor'+'s'+'o'='TORSO'
Can you help me to learn more?
(Other definitions for torso that I've seen before include "Body's trunk" , "Roost (anag)" , "Poorly-dressed child" , "Body without head, neck and limbs" , "Body's core" .)