 The octopus also has large blood sinuses around its gut and behind its eyes that function as reserves in times of physiologic stress.The octopus' heart rate does not change significantly with exercise, though temporary cardiac arrest of the systemic heart can be induced by oxygen debt, almost any sudden stimulus, or mantle pressure during jet propulsion.Its only compensation for exertion is through an increase in stroke volume of up to three times by the systemic heart, which means it suffers an oxygen debt with almost any rapid movement.