heart vs city center

heart and city center both are nouns.

Word	Noun	Adjective	Verb	Adverb
heart	Yes	No	No	No
city center	Yes	No	No	No

As nouns, city center is a hyponym of heart; that is, city center is a word with a more specific, narrower meaning than heart:

heart (noun)	city center (noun)
a playing card in the major suit that has one or more red hearts on it	the central part of a city
the courage to carry on
an inclination or tendency of a certain kind
the hollow muscular organ located behind the sternum and between the lungs; its rhythmic contractions move the blood through the body
the locus of feelings and intuitions
the choicest or most essential or most vital part of some idea or experience
a positive feeling of liking
a firm rather dry variety meat (usually beef or veal)
an area that is approximately central within some larger region
a plane figure with rounded sides curving inward at the top and intersecting at the bottom; conventionally used on playing cards and valentines