pounding vs heartbeat

pounding and heartbeat both are nouns.

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

As nouns, heartbeat is a hypernym of pounding; that is, heartbeat is a word with a broader meaning than pounding:

pounding: an instance of rapid strong pulsation (of the heart)
heartbeat: the rhythmic contraction and expansion of the arteries with each beat of the heart

Other hypernyms of pounding include beat, pulsation, pulse.

pounding (noun)	heartbeat (noun)
the act of pounding (delivering repeated heavy blows)	an animating or vital unifying force
repeated heavy blows	the rhythmic contraction and expansion of the arteries with each beat of the heart
an instance of rapid strong pulsation (of the heart)	a very short time (as the time it takes the eye to blink or the heart to beat)