The role of some endogenous bioregulators in formation of cardiogenic reflectory effects on circulation were investigated in acute experiments on anesthetized animals with using various methods (direct recording of impulse activity from cardiac afferent nerves, humoral isolation of the heart). Interrelations between development of cardiogenic depressor reactions and nitric oxide production was established. Systemic inhibition of NOS led to decrease in dilatation of coronary and peripheral vessels. At the other hand dramatic suppression of cardiogenic depressor reflexes followed by inhibition of prostacyclin production. The data support the essential role of endogenous bioactive substances in formation of cardiogenic reflex effects on circulation in physiological and pathological states. We also suggest that a mayor metabolite of arachidonic acid--prostacyclin--is modulator and one of humoral components of the vagus-mediated cardiogenic depressor reflex in physiological conditions.