heart surgeon vs specialist

heart surgeon and specialist both are nouns.

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

As nouns, specialist is a hypernym of heart surgeon; that is, specialist is a word with a broader meaning than heart surgeon:

heart surgeon: a specialist in cardiology; a specialist in the structure and function and disorders of the heart
specialist: practices one branch of medicine

Other hypernyms of heart surgeon include medical specialist.

heart surgeon (noun)	specialist (noun)
a specialist in cardiology; a specialist in the structure and function and disorders of the heart	an expert who is devoted to one occupation or branch of learning
	practices one branch of medicine