Scintigraphic images of myocardial iodine 123-labeled metaiodobenzylguanidine (MIBG) reflect the relative distribution of adrenergic neurodensity and function in the myocardium. In patients with hypertrophic cardiomyopathy or after infarction, MIBG uptake in hypertrophied myocardium and the infarct-related myocardium was found to be decreased in comparison to blood flow distribution, delineated with thallium 201. Most intriguingly, semiquantitative measurements in patients with congestive heart failure demonstrated reduced myocardial MIBG uptake. This reduction correlated directly with indexes of left ventricular function. Decreases in neuronal density, dysfunction of adrenergic neurons, or chronically elevated circulating norepinephrine levels may account for this diminished myocardial uptake, which, as demonstrated in a pilot study of 90 patients with congestive heart failure, was found to be of predictive value for survival.