BackgroundKidney dysfunction (KD) is a main limiting factor of applying guideline‐directed medical therapy (GDMT) and reaching the recommended target doses (TD) in heart failure (HF) with reduced ejection fraction (HFrEF).HypothesisWe aimed to assess the success of optimization, long‐term applicability, and adherence of neurohormonal antagonist triple therapy (TT:RASi [ACEi/ARB/ARNI] + βB + MRA) according to the KD after a HF hospitalization and to investigate its impact on prognosis.MethodsThe data of 247 real‐world, consecutive patients were analyzed who were hospitalized in 2019−2021 for HFrEF and then were followed‐up for 1 year. The application and the ratio of reached TD of TT at hospital discharge and at 1 year were assessed comparing KD categories (eGFR: ≥90, 60−89, 45−59, 30−44, <30 mL/min/1.73 m2). Moreover, 1‐year all‐cause mortality and rehospitalization rates in KD subgroups were investigated.ResultsMajority of the patients received TT at hospital discharge (77%) and at 1 year (73%). More severe KD led to a lower application ratio (p < .05) of TT (92%, 88%, 80%, 73%, 31%) at discharge and at 1 year (81%, 76%, 76%, 68%, 40%). Patients with more severe KD were less likely (p < .05) to receive TD of MRA (81%, 68%, 78%, 61%, 52%) at discharge and a RASi (53%, 49%, 45%, 21%, 27%) at 1 year.One‐year all‐cause mortality (14%, 15%, 16%, 33%, 48%, p < .001), the ratio of all‐cause rehospitalizations (30%, 35%, 40%, 43%, 52%, p = .028), and rehospitalizations for HF (8%, 13%, 18%, 20%, 38%, p = .001) were significantly higher in more severe KD categories.ConclusionsKD unfavorably affects the application of TT in HFrEF, however poorer mortality and rehospitalization rates among them highlight the role of the conscious implementation and up‐titration of GDMT.