Background <p>The neutrophil-to-lymphocyte ratio (NLR) reflects systemic inflammation. Whether higher NLR is associated with subsequent kidney failure among critically ill patients with heart failure (HF) remains uncertain.</p> Methods <p>Using MIMIC-IV v3.1, we identified 3,368 ICU patients with HF. Baseline NLR was analyzed as tertiles and as a continuous variable (raw NLR and ln[NLR]). Cause-specific Cox proportional hazards models were used to estimate associations with 1-year kidney failure (with deaths as a competing event), 1-year all-cause mortality, and kidney failure over the entire follow-up.</p> Results <p>Over 1&#xa0;year, 293/3,368 (8.7%) developed kidney failure. Higher NLR was associated with greater kidney-failure risk. Compared with the lowest tertile, the highest tertile had a higher hazard of 1-year kidney failure (HR 1.61, 95% CI 1.20–2.15). As a continuous exposure, ln(NLR) was associated with kidney failure at 1&#xa0;year (HR 1.26, 95% CI 1.10–1.43) and over the entire follow-up (HR 1.22, 95% CI 1.09–1.37). For mortality, ln(NLR) was associated with higher 1-year all-cause mortality (HR 1.32, 95% CI 1.23–1.41) and the highest tertile showed greater risk versus the lowest (HR 1.79, 95% CI 1.52–2.10).</p> Conclusion <p>Among ICU patients with HF, higher baseline NLR was associated with greater hazards of kidney failure and all-cause mortality. More studies are required to confirm these findings.</p>