Introduction. We investigated the early signs of reverse cardiac remodeling in symptomatic patients with heart failure (HF) with reduced left ventricular ejection fraction (LVEF) during one-month, low dose add-on sacubitril/valsartan (S/V) therapy. Material and Methods. Thirty-seven adult patients with HF were evaluated before and after one-month treatment with a low dose (24/26 mg BID) of S/V. Results. The patients' mean age was 64.50 ± 17.50 years and median LVEF 29.10%. The S/V treatment resulted in a significant decrease in blood levels of the N-terminal pro-B-type natriuretic peptide (-364 pg/mL; p = 0.01), left ventricular end-diastolic (-2 mm; p < 0.01) and end-systolic diameters (-2.4 mm; p = 0.01), end-diastolic (-9 ml; p < 0.01) and end-systolic volumes (-6 ml; p < 0.01), the indexed left atrial volume (-8 ml/m²; p < 0.01), effective orifice area mitral regurgitation (-0.09 cm2; p = 0.03). The left ventricular ejection fraction did not change in the course of the study. Conclusion. One-month, low dose add-on S/V therapy in patients with HF and reduced LVEF induces reverse cardiac remodeling. The long-term effects of a low dose S/V add-on therapy in this group of patients requires further research. [ABSTRACT FROM AUTHOR]