The aim of this study was to determine how sacubitril/valsartan compared with valsartan in an outpatient setting affects left ventricular remodeling in heart failure with reduced ejection fraction and functional (or secondary) mitral regurgitation (SMR) due to the effect of dual inhibition of the renin-angiotensin system and neprilysin. The outpatient study included 90 patients with chronic SMR who were followed up for 12 months. They received sacubitril/valsartan or valsartan instead of the more commonly used angiotensin-converting enzyme inhibitor enalapril for heart failure, in addition to standard medical therapy for heart failure. The difference in NT-proBNP change between groups was the primary endpoint. Changes in effective regurgitation orifice area, left ventricular ejection fraction, left ventricular end-systolic and end-diastolic volume indices, left atrial volume index, E/e' index, and exercise tolerance on the 6-minute walk test were secondary endpoints. In the treatment efficacy analysis, NT-proBNP levels decreased significantly by 37% in the sacubitril/valsartan group and by 11% in the valsartan group (P<0.001). Ejection fraction and exercise tolerance (increase in walking distance in the 6-min test) increased in the sacubitril/valsartan group (P<0.05). Also, in this group, the effective area of the regurgitation orifice, the left atrial volume index, the E/e' index, and the indices of the end-systolic and end-diastolic volume of the left ventricle (P<0.05) decreased more pronouncedly. Compared with valsartan, treatment with sacubitril/valsartan led to a significant improvement in cardiac remodeling in patients with SMR and heart failure with reduced ejection fraction.