cardiologist vs heart surgeon

cardiologist and heart surgeon both are nouns.

Word	Noun	Adjective	Verb	Adverb
cardiologist	Yes	No	No	No
heart surgeon	Yes	No	No	No

As nouns, cardiologist and heart surgeon are synonyms defined as:

cardiologist and heart surgeon: a specialist in cardiology; a specialist in the structure and function and disorders of the heart

Other synonyms of cardiologist include heart specialist.

cardiologist (noun)	heart surgeon (noun)
a specialist in cardiology; a specialist in the structure and function and disorders of the heart	a specialist in cardiology; a specialist in the structure and function and disorders of the heart