6-Hydroxydopamine was injected into normotensive rats (NR) and spontaneously hypertensive rats (SHR) during three weeks after birth. Cardiac output, blood pressure and heart contractility were measured in NR and SHR aged ten weeks. Sympathectomized SHR did not develop arterial hypertension. In these rats, cardiac output and heart contractility were decreased, whereas in sympathectomized NR, blood pressure was unchanged and cardiac output was increased. Possible mechanisms of the hemodynamic data are discussed.