Buck's pretty empty-headed plaything, warm hearted, American (6)
I believe the answer is:
dollar
'buck's' is the definition.
(slang term for a dollar)
'plaything warm hearted american' is the wordplay.
'plaything' becomes 'doll' (doll is a kind of plaything).
'warm hearted american' becomes 'ar' (I can't justify this - if you can you should give a lot more credence to this answer).
'doll'+'ar'='DOLLAR'
'pretty empty-headed' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for dollar that I've seen before include "Philip -, English poet" , "Foreign currency" , "Australian currency" , "US monetary unit" , "Monetary unit in several countries" .)