rather, their function in regulating blood flow is parasitic on the fact that the proper function of hearts is to pump blood.
(their function in regulating blood flow; is; parasitic on the fact that the proper function of hearts is to pump blood) (the proper function of hearts; is; to pump blood)
their function in regulating blood flow the proper function of hearts
is is
parasitic on the fact that the proper function of hearts is to pump blood
to pump blood