Banking organisation's heads upset rival currency (7)
I believe the answer is:
bolivar
'currency' is the definition.
(currency of Venezuela)
'banking organisation's heads upset rival' is the wordplay.
'heads' indicates taking the first letters.
'upset' is an anagram indicator.
The first letters of 'banking organisations' is 'bo'.
'rival' anagrammed gives 'livar'.
'bo'+'livar'='BOLIVAR'
(Other definitions for bolivar that I've seen before include "Simon --, South American liberator" , "Foreign brass" , "Basic unit of money in Venezuela" , "Currency of Venezuela" , "Founder of Bolivia" .)