heartbeat vs systole

heartbeat and systole both are nouns.

Word	Noun	Adjective	Verb	Adverb
heartbeat	Yes	No	No	No
systole	Yes	No	No	No

As nouns, systole is a hyponym of heartbeat; that is, systole is a word with a more specific, narrower meaning than heartbeat:

heartbeat: the rhythmic contraction and expansion of the arteries with each beat of the heart
systole: the contraction of the chambers of the heart (especially the ventricles) to drive blood into the aorta and pulmonary artery

Other hyponyms of heartbeat include diastole, pounding, throb, throbbing.

heartbeat (noun)	systole (noun)
an animating or vital unifying force	the contraction of the chambers of the heart (especially the ventricles) to drive blood into the aorta and pulmonary artery
the rhythmic contraction and expansion of the arteries with each beat of the heart
a very short time (as the time it takes the eye to blink or the heart to beat)