What sweetheart shows heart? (4)
I believe the answer is:
core
'heart?' is the definition.
('core' can be a synonym of 'heart')
'what sweetheart' is the wordplay.
'what' becomes 'cor' (I can't explain this - if you can you should give a lot more credence to this answer).
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'cor'+'e'='CORE'
'shows' is the link.
Can you help me to learn more?
(Other definitions for core that I've seen before include "The centre of an object" , "Nucleus" , "Drilled rock sample" , "The centre part, as of an apple" , "Kernel" .)