megalocardia vs cardiomegaly

megalocardia and cardiomegaly both are nouns.

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

As nouns, megalocardia and cardiomegaly are synonyms defined as:

Other synonyms of megalocardia include enlarged heart, megacardia.

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