Cardiac sympathetic nerve stimulation produces increases in various indices of cardiac work and metabolism. To determine how these increased O2 demands are met, the effects of stimulation of the ansa subclavia on regional arterial and venous O2 saturation, O2 extraction, blood flow, and O2 consumption were determined in the hearts of 16 pentobarbital-anesthetized open-chest dogs. Microspectrophotometric observations of small regional arteries and veins in quick-frozen hearts to determine regional O2 extraction were combined with regional blood flow measurements with radioactive microspheres to determine regional myocardial O2 consumption by the Fick principle. Ansa subclavia stimulation produced significant increases in maximum rate of pressure development, heart rate, and blood pressure. Under control conditions, venous O2 saturation was lower and O2 extraction higher in the subendocardial compared with the subepicardial region of the left ventricle. While sympathetic stimulation did not alter the mean O2 extraction or venous O2 saturation values, there were no longer significant subepicardial vs. subendocardial differences in these parameters. Flow and O2 consumption in these regions increased proportionally during stimulation. The ratio of O2 supply to O2 consumption was not significantly altered by ansa subclavia stimulation, indicating that sympathetic stimulation produced no adverse effect in either region.