Capital head pulse (4,4)
I believe the answer is:
lima bean
'pulse' is the definition.
(I've seen this before)
'capital head' is the wordplay.
'capital' becomes 'lima' (capital of Peru).
'head' becomes 'bean' (bean is a kind of head).
'lima'+'bean'='LIMA BEAN'
(Other definitions for lima bean that I've seen before include "Be animal (anag)" , "vegetable" , "Pulse" , "F - with 12a" , "food supplier" .)