atrium vs atrium cordis

atrium and atrium cordis both are nouns.

Word	Noun	Adjective	Verb	Adverb
atrium	Yes	No	No	No
atrium cordis	Yes	No	No	No

As nouns, atrium cordis is a hyponym of atrium; that is, atrium cordis is a word with a more specific, narrower meaning than atrium:

atrium: any chamber that is connected to other chambers or passageways (especially one of the two upper chambers of the heart)
atrium cordis: the upper chamber of each half of the heart

Other hyponyms of atrium include atrium of the heart.

atrium (noun)	atrium cordis (noun)
the central area in a building; open to the sky	the upper chamber of each half of the heart
any chamber that is connected to other chambers or passageways (especially one of the two upper chambers of the heart)