heaving vs external respiration

heaving and external respiration both are nouns.

Word	Noun	Adjective	Verb	Adverb
heaving	Yes	No	No	No
external respiration	Yes	No	No	No

As nouns, external respiration is a hypernym of heaving; that is, external respiration is a word with a broader meaning than heaving:

heaving: breathing heavily (as after exertion)
external respiration: the bodily process of inhalation and exhalation; the process of taking in oxygen from inhaled air and releasing carbon dioxide by exhalation

Other hypernyms of heaving include breathing, respiration, ventilation.

heaving (noun)	external respiration (noun)
throwing something heavy (with great effort)	the bodily process of inhalation and exhalation; the process of taking in oxygen from inhaled air and releasing carbon dioxide by exhalation
breathing heavily (as after exertion)
the act of lifting something with great effort
an upward movement (especially a rhythmical rising and falling)