Heart failure (HF) is a progressive condition with an increasing prevalence, and the scientific evidence of heart failure with reduced ejection fraction (HFrEF) reports a 6% rate of 1-year mortality in stable patients, whereas, in recently hospitalized patients, the 1-year mortality rates exceed 20%. The Sacubitril/Valsartan (S/V), the first angiotensin receptor neprilysin inhibitor (ARNI), significantly reduced both HF hospitalization and cardiovascular mortality. Aim of the study: to evaluate the effect of S/V in a follow-up period of 5 years from the beginning of the therapy. We compared the one-year outcomes of S/V use with those obtained after 5 years of therapy, monitoring the long-term effects in a real-world population with HFrEF. Methods: Seventy consecutive patients with HFrEF and eligible for ARNI, according to PARADIGM-HF criteria, were enrolled. All patients had an overall follow-up of 60 months, during which time they underwent standard transthoracic echocardiography (TTE) with Global Longitudinal Strain (GLS) evaluation, the Kansas City Cardiomyopathy Questionnaire (KCCQ), the Six Minutes Walking Test (6MWT), and blood tests (NT-pro-BNP and BNP, renal function tests). Results: NTproBNP values were reduced significantly among the three time-points (p < 0.001). Among echocardiographic parameters, left ventricle end-diastolic volume (LV EDV) and E/e’ significantly were reduced at the first evaluation (12 months), while left ventricle end-systolic volume (LV ESV) decreased during all follow-ups (p < 0.001). LV EF (p < 0.001) and GLS (p < 0.001) significantly increased at both evaluations. The 6MWT (p < 0.001) and KCCQ scores (p < 0.001) increased significantly in the first 12 months and remained stable along the other time-points. NYHA class showed an increase in class 1 subjects and a decrease in class 3 subjects during follow-up. NTproBNP, BNP, 6MWT, and KCCQ scores showed a significant change in the first 12 months, while LVEF, GLS, and ESV changed during all evaluations. Conclusions: We verified that the improvements obtained after one year of therapy had not reached a plateau phase but continued to improve and were statistically significant at 5 years. Although our data should be confirmed in larger and multicentre studies, we can state that the utilization of Sacubitril/Valsartan has catalysed substantial transformations in the prognostic landscape of chronic HFrEF, yielding profound clinical implications.