megacardia vs cardiomegaly

megacardia and cardiomegaly both are nouns.

Word	Noun	Adjective	Verb	Adverb
megacardia	Yes	No	No	No
cardiomegaly	Yes	No	No	No

As nouns, megacardia and cardiomegaly are synonyms defined as:

Other synonyms of megacardia include enlarged heart, megalocardia.

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