Heart attack (8)
I believe the answer is:
coronary
'heart attack' is the definition.
(coronary is a kind of heart attack)
This is all the clue.
(Other definitions for coronary that I've seen before include "Obstruction of blood flow in an artery" , "Of the arteries that supply the heart" , "O, can Rory cope with a heart attack?" , "Of the arteries supplying blood to heart" , "The blood vessels around the heart" .)