Background: Use of medical therapies for heart failure (HF) patients with moderate kidney dysfunction is low. We hypothesized that lack of initiation of HF therapy reflects the clinicians’ reluctance in very elderly and frail patients more than kidney dysfunction itself. Methods: HF patients were identified from nationwide registers between 2014 and 2021. Information was obtained on eGFR, frailty status, and prescription of HF therapy. Patients were divided into three groups: normal kidney function (eGFR ≥ 60); moderate kidney dysfunction (GFR between 30 and 59); and severe kidney dysfunction (GFR < 30). Multivariate Cox models were used to study the association of eGFR, age, and frailty with use of HF therapy. Results: Of the 42,320 HF patients included those with lower eGFR were significantly older and frailer (median age 74.3 years and 37.8% frail). The crude initiation rate of all three drug classes decreased with decreasing eGFR in a stepwise fashion. After adjusting for age and frailty status, initiation of MRA decreased with decreasing kidney function (moderate kidney function HR 0.80(95% CI 0.77–0.84) and severe kidney function HR 0.24(0.21–0.27)). After adjusting for age and frailty status, initiation of RAS inhibitor and BB was not significantly lower for moderate kidney dysfunction (HR 0.97(0.93–1.02), and HR 1.06(0.97–1.16, respectively)). Initiation of RAS inhibitor was significantly lower for patients with severe kidney dysfunction, HR 0.45(0.41–0.50), but not for BB initiation HR 1.09(1.05–1.14). Conclusion: In a real-world HF cohort, patients with moderate and severe kidney dysfunction were associated with reduced use of MRA irrespective of age and frailty. Reduced use of RASi was associated with severe kidney dysfunction, whereas for patients with moderate kidney dysfunction, reduced use was mainly driven by aging and frailty. Reduced use of BB seemed to be primarily explained by aging and frailty.