Relative significance of cardiac and vessel components as well as the role of arachidonic acid metabolites in the development of endotoxic shock have been investigated in two series of experiments on the mongrel dogs. It is determined that endotoxin exerts no direct negative inotropic influence on the myocardium: blood pool in peripheral capacitance vessels plays a main role in the development of the first phase of the endotoxic shock (the first 30 min), that is a result of prostacyclin influence on these vessels, while in the subsequent phase it is a result of the bloodflow disturbance in the myocardium or arachidonic acid metabolites influence on the myocardium. Administration of endotoxin to the bloodflow significantly increased concentration of prostanoids; thromboxane A2 and prostacyclin in it. Indomethacin, inhibitor of prostaglandin synthesis, prevents development of the endotoxic shock.