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