atrium of the heart vs atrium

atrium of the heart and atrium both are nouns.

Word	Noun	Adjective	Verb	Adverb
atrium of the heart	Yes	No	No	No
atrium	Yes	No	No	No

As nouns, atrium is a hypernym of atrium of the heart; that is, atrium is a word with a broader meaning than atrium of the heart:

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

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