This study assessed the prognostic value of Iodine-123-metaiodobenzylguanidine (MIBG) imaging and of the plasma level of cardiac natriuretic peptides in patients with left ventricular dysfunction resulting from cardiomyopathy. Predictors of cardiac death or hospitalization related to progressive heart failure were examined in 171 patients with chronic heart failure (96 patients with idiopathic cardiomyopathy and 75 patients with ischemic cardiomyopathy). All patients underwent MIBG imaging at rest and other hemodynamic studies. During a mean (±SD) follow-up period of 27±11 months, 11 patients died from heart failure and 16 required hospitalization. High MIBG washout was an independent predictor of cardiac death (relative risk [RR] = 1.158, p<0.0001) whereas the plasma level of brain natriuretic peptide (BNP: relative risk [RR] = 1.005, p<0.0001) and high MIBG washout (relative risk [RR] = 1.094, p<0.0001) were predictors of progressive heart failure (ie, combined cardiac death and hospitalization). Accelerated myocardial adrenergic nerve activity as assessed by MIBG imaging and the plasma levels of BNP are powerful predictors of the patient's prognosis. (Jpn Circ J 2001; 65: 155 - 160)