Chamber of the heart (9)
(Other definitions for ventricle that I've seen before include "One of four heart chambers" , "bloody pump!" , "Chamber in organ of body - the heart has two" , "Heart cavity that pumps blood to arteries" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">chamber of the heart</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for atrium that I've seen before include "lobby" , "Central court of ancient Roman house" , "One of the two upper chambers of the heart" , "Central hall or court" , "High central hall in large building" .)