President in black American hearts (4)
I believe the answer is:
bush
'president' is the definition.
(George H W Bush or George W Bush)
'black american hearts' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'american' becomes 'US' (abbreviation for United States).
'hearts' becomes 'h' (abbreviation used in card games e.g. bridge).
'b'+'us'+'h'='BUSH'
'in' acts as a link.
(Other definitions for bush that I've seen before include "Shrub; protective sleeve" , "Shrub; Kate --, singer" , "Shrub; US president" , "ex-president" , "Shrub; wild vegetation" .)