megacardia vs enlarged heart

megacardia and enlarged heart both are nouns.

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

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

Other synonyms of megacardia include cardiomegaly, megalocardia.

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