AIM: To compare effects of therapy with angiotensin converting enzyme inhibitor quinapril (Q), angiotensin II receptor antagonist valsartan (V), and their combination in patients with stable moderate chronic heart failure (CHF). MATERIAL AND METHODS: Patients (n=80) with NYHA class II-III CHF due to ischemic heart disease, dilated cardiomyopathy or decompensated hypertensive heart and ejection fraction <40% were randomized into 3 groups. Patients of group Q, V and Q+V received Q (average dose 13 mg/day, n=28), V (121 mg/day, n=26), and combination of Q and V (12 and 78 mg/day, n=26), respectively. Methods included assessment of clinical state and quality of life, echocardiography, 6 min walk test, Holter ECG monitoring with measurements of parameters of heart rate variability (HRV), and determination of neurohormones in peripheral blood. Examinations and measurements were made at baseline, in 3 and 6 months. RESULTS AND CONCLUSIONS: Six months therapy with Q, V and their combination resulted in improvement of clinical and functional state of patients. More pronounced augmentation of exercise tolerance and lowering of CHF functional class were observed in group Q. Combined use of Q and V had no significant advantages over monotherapy with Q and V when effect on parameters of left ventricular remodeling were concerned. Therapy with Q was associated with "escape" of blockade of aldosterone synthesis and "reactivation" of angiotensin II formation after 6 months. The use of V and combination of V+Q allowed to achieve more stable but incomplete control of aldosterone activity. The use of Q appears to be the preferential regimen to influence activity of sympathoadrenal system and parameters of 24 hour HRV compared with V and Q+V. Long term therapy with V does not improve main parameters of 24 hour HRV.