A steadily increasing dose of norepinephrine given to rats for 7 consecutive days (cumulative dose 25 mg/kg) resulted in the development of focal necrotic areas with abundant collagen fibers, marked hypertrophy of cardiomyocytes and a mild depletion of the myocardial level of high-energy phosphates. These changes were associated with a more than two-fold decrease in the external work of the isolated rat heart at a moderate functional load, that may be attributed mainly to limited filling of the left ventricle due to elevated diastolic pressure and increased diastolic stiffness. If 100 mg/kg taurine was given daily before the dose of norepinephrine, the functional and metabolic alterations induced by norepinephrine were significantly reduced. The external work of the isolated heart was 1.5 times higher when taurine was added than it was when the animals were treated with norepinephrine alone; and there was a significant reduction in the increase in left ventricular diastolic pressure and stiffness. The ability of the heart to respond to the injection of a bolus of Ca2+ by decreasing the minimal left ventricular diastolic pressure was almost lost after treatment with norepinephrine alone, but was partly restored when taurine was added. Taurine also prevented the occurrence of necrosis as well as depletion of the levels of myocardial ATP and phosphocreatine; while the extent of an increase in cellular diameter and the area of extracellular space was roughly the same as without taurine.