Myocardial infarct (5,6)
I believe the answer is:
heart attack
'myocardial infarct' is the definition.
(I know that myocardial infarct can be written as heart attack)
This is all the clue.
(Other definitions for heart attack that I've seen before include "Sudden severe cardiac malfunction" , "Heat at track (anag) - a potential killer!" , "Coronary" .)