The interaction of physiologic variables that appear to be predictive of prognosis in patients with severe congestive heart failure was examined in a series of 139 patients referred to a heart failure service. Left ventricular ejection fraction, peak oxygen consumption during a progressive maximal exercise test and resting plasma norepinephrine concentration were identified as the strongest univariate predictors of prognosis. Examination of their interaction was accomplished by stratifying each variable into quartiles and then pooling quartiles for bivariate analysis. The data demonstrate that ejection fraction has the most profound effect on survival calculated from maximal oxygen consumption and norepinephrine concentration, but that each of the variables provides additional independent prognostic information when added to survival estimated from any of the other variables. Therefore, ventricular function, exercise tolerance and sympathetic nervous system activation appear to provide independent insight into the prognosis of patients with heart failure.