heart attack vs heart failure

heart attack and heart failure both are nouns.

Word	Noun	Adjective	Verb	Adverb
heart attack	Yes	No	No	No
heart failure	Yes	No	No	No

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

heart attack: a sudden severe instance of abnormal heart function
heart failure: inability of the heart to pump enough blood to sustain normal bodily functions

Other hypernyms of heart attack include attack, coronary failure.

heart attack (noun)	heart failure (noun)
a sudden severe instance of abnormal heart function	inability of the heart to pump enough blood to sustain normal bodily functions