Entrance hall showing a bit of heart (6)

I believe the answer is:

atrium

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'entrance hall' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for atrium that I've seen before include "One of the two upper chambers of the heart" , "An upper chamber of the heart" , "Central hall of shopping mall etc" , "Central courtyard" , "Central court/hall" .)

I've seen this clue in The Daily Express.

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