Cardiovascular effects of dobutamine (DOB), isoproterenol (Iso), and dopamine (DA) were compared in Beagle dogs weighing 6.8 to 11.6 kg under experimental shock produced by ligation of the left coronary arteries and intravenous administration of hexamethonium-Br (10 mg/kg). Intravenous infusion of DOB (1 approximately 20 microgram/kg/min) dose-dependently improved the hemodynamic state of shock by increasing left ventricular dp/dt (LV dp/dt), cardiac output (CO), and blood pressure. These improvements were also observed with the infusion of DA (20 approximately 40 microgram/kg/min). However, the improvement with Iso (0.01 approximately 0.2 microgram/kg/min) was incomplete because of the marked fall of total peripheral resistance. Both DOB and DA increased the venous return, pressure in the inferior vanae cavae, and pressure difference between venous pressure and left ventricular end diastolic pressure. It was presumed that these effects were related to the stimulation of the alpha receptor in the venous system, in addition to the marked positive inotropic effects by DOB or DA. Iso increased significantly only the venous return. Although increases of coronary flow with DOB and DA are probably mainly due to an increase of myocardial oxygen consumption, the increase of coronary perfusion pressure also may contribute to the increase of coronary flow. As a result, myocardial oxygen balance was improved with DOB or DA. alpha stimulation in the venous system as well as beta 1 stimulation apparently contributes to improvement of the deteriorated hemodynamic state, in experimental shock, as induced in dogs.