Fool; artery problem (4)
I believe the answer is:
clot
This clue is a double definition.
'fool' is the first definition.
(I've seen this before)
'artery problem' is the second definition.
(I've seen this in another clue)
(Other definitions for clot that I've seen before include "Coagulate - fool" , "3 [DUMMY]" , "A lump in a blood vessel" , "Clumsy person" , "Curdle - idiot" .)