cardiology vs medical specialty

cardiology and medical specialty both are nouns.

Word	Noun	Adjective	Verb	Adverb
cardiology	Yes	No	No	No
medical specialty	Yes	No	No	No

As nouns, medical specialty is a hypernym of cardiology; that is, medical specialty is a word with a broader meaning than cardiology:

cardiology: the branch of medicine dealing with the heart and its diseases
medical specialty: the branches of medical science that deal with nonsurgical techniques

Other hypernyms of cardiology include medicine.

cardiology (noun)	medical specialty (noun)
the branch of medicine dealing with the heart and its diseases	the branches of medical science that deal with nonsurgical techniques