Upper chamber of the heart (7)
I believe the answer is:
auricle
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">upper chamber of the heart</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for auricle that I've seen before include "Technical name for the external ear" , "External part of the ear" , "Air clue for part of the ear" , "place in one's heart" , "atrium" .)