Of the heart (7)
I believe the answer is:
cardiac
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">of the heart</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for cardiac that I've seen before include "Appertaining to the heart" , "Sort of surgery" , "Pertaining to the heart" , "Relating to the heart" , "Relating to 8 down, part one" .)