The inotropic effects consequent to the elevation of arterial pressure by infusion of angiotensin II were studied in dogs with intact autonomic nervous systems and in dogs previously submitted to ganglionic blockade. Maximal velocity of contraction (VmaxTP) was used to evaluate the inotropic state. When the heart rate was allowed to vary or when it was maintained constant by atrial stimulation the rise in blood pressure was accompanied by impaired contractility in the animals with intact nervous sytem. This negative inotropic influence seems to be due to changes of the neurovegetative tone due to baroreceptor reflexes. In the dogs submitted to ganglionic blockade, during the administration of the drug, there was elevation of VmaxTP. The improved inotropic state in these animals was explained by adrenergic hyperactivity produced by the polypeptide.