heartbeat vs mo

heartbeat and mo both are nouns.

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

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

heartbeat: a very short time (as the time it takes the eye to blink or the heart to beat)
mo: an indefinitely short time

Other hypernyms of heartbeat include bit, minute, moment, second.

heartbeat (noun)	mo (noun)
an animating or vital unifying force	an indefinitely short time
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)