Crossword Genius

Either of the two upper chambers of the heart (6)

Ross

I believe the answer is:

atrium

(Other definitions for atrium that I've seen before include "Um, I rat on the chamber of the heart" , "Entrance hall" , "An upper cavity in the heart" , "Central area in a building, open or with a glass roof" , "Central court of ancient Roman house" .)

I've seen this clue in The Times.
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