The purpose of this study was to identify the factor(s) that characterize impaired glomerular filtration rate (GFR) in congestive heart failure (CHF) patients. We studied 34 patients, measuring systemic hemodynamics, vasoactive hormones, and sodium and volume status. Renal plasma flow (para-aminohippurate) and GFR (inulin) were assessed by steady-state clearance techniques. Both linear and multiple regression analyses were performed. Impaired GFR was characterized by reduction of renal blood flow and renal fraction of cardiac output, and by an increase of renal vascular resistance. The correlation between GFR and filtration fraction (r = 0.492, P less than 0.003) indicated that individuals with greatest impairment of GFR had the lowest filtration fraction and increased overall renal vascular resistance, indicating dependence of GFR on afferent, rather than efferent vasoconstriction, under conditions of low renal perfusion. Mean vasoactive hormones and blood volume were increased, but without clear cut correlation with GFR. The greatest impairment of GFR was observed in elderly CHF patients, as renal blood flow and function demonstrated an age-dependent decline, in addition to the adverse effects of CHF. In a multiple regression model, renal blood flow and filtration fraction accounted for 69% and 25%, respectively, of the variability of GFR, with a co-linear influence of age. Thus, we have identified age-related, abnormal renal hemodynamic patterns in CHF, and the fragile nature of GFR in the elderly CHF population.