enlarged heart vs megacardia

enlarged heart and megacardia both are nouns.

Word	Noun	Adjective	Verb	Adverb
enlarged heart	Yes	No	No	No
megacardia	Yes	No	No	No

As nouns, enlarged heart and megacardia are synonyms defined as:

Other synonyms of enlarged heart include cardiomegaly, megalocardia.

enlarged heart (noun)	megacardia (noun)
an abnormal enlargement of the heart	an abnormal enlargement of the heart