Using the tracer microsphere technique, the effect of circumflex artery ligation on regional myocardial perfusion was studied in 8 ventricles which had been sympathectomized 2 weeks earlier and in 9 nonsympathectomized controls. Preocclusion flow values in the chronically sympathectomized ventricles were approximately 75% of those in the controls even though heart rate and arterial pressure were maintained at the same levels in the 2 groups. After circumflex artery ligation, flow to the central ischemic region was slightly greater in the sympathectomized ventricle, but this difference was not statistically significant. However, in the ischemic region adjacent to the central ischemic region, flows in the chronically sympathectomized ventricle were 250--450% of those in the nonsympathectomized ventricle. When these flows were normalized to the preocclusion values, these differences were even greater. Thus, following circumflex artery occlusion, ischemic perfusion of the chronically sympathectomized myocardium is substantially improved.