The aim of this study was to highlight a different hormonal and hemodynamic pattern in patients with mild cardiomyopathy. For this purpose, we studied subjects with mild heart failure (CHF; NYHA class I and II; post-ischemic and idiopathic) who underwent an isotonic saline load (SL) (0.22 ml/kg/min of 0.9% NaCl for 120 min). A second group of age- and sex-matched normal subjects (C) was studied as a control. Basal hormonal and hemodynamic values of the 2 groups differed only in atrial natriuretic factor (ANF), left ventricular end-diastolic diameter and ejection fraction (EF). There were, on the contrary, no differences in basal plasma renin activity (PRA) and plasma aldosterone (PA) values. After SL, in C, percent changes in EF, cardiac output and ANF values were significantly higher than in CHF while total peripheral resistances increased only in CHF but not in C. In both groups there were decrements of PRA and PA, but these responses were significantly higher in C than in CHF. In conclusion, our results show that hormonal, renal and hemodynamic responses to salt/volume load are compromised in the early asymptomatic phase of heart failure. These abnormalities may predict the progressive deterioration of cardiac function, and may indicate appropriate therapeutic interventions since the early phases of the disease.