OBJECTIVE: To evaluate the effectiveness of the lactate/serum albumin (L/A) ratio in predicting 30- and 90-day all-cause mortality and 30-day all-cause readmissions in patients presenting to the emergency department (ED) with acute heart failure (AHF). STUDY DESIGN: An observational study. Place and Duration of the Study: Department of Emergency, Kocaeli Derince Training and Research Hospital and Kocaeli City Hospital, Turkiye, from November 2022 to October 2023. METHODOLOGY: Patients diagnosed with heart failure in the ED were prospectively enrolled. Demographic and clinical data, including serum lactate and albumin levels, were recorded at admission. The L/A ratio was calculated, and its association with 30- and 90-day all-cause mortality and 30-day all-cause hospital readmission was examined. Receiver operating characteristic (ROC) analysis was used to assess its predictive performance. RESULTS: A total of 410 patients were included. The L/A ratio showed statistical significance for predicting 30-day all-cause mortality but lacked clinical reliability. At a cut-off value of ≥0.85, sensitivity was 66.15%, specificity was 53.04%, and the area under the ROC curve (AUC) was 0.647. At ≥0.61, sensitivity was 56.3%, specificity was 66.32%, and AUC was 0.635. No significant relationship was found between the L/A ratio and 30-day all-cause readmissions. In multivariable logistic regression analysis, the L/A ratio remained independently associated with 30-day all-cause mortality (OR: 2.48, 95% CI: 1.33-4.60, p = 0.004). CONCLUSION: The L/A ratio was not a clinically reliable predictor of 30- and 90-day all-cause mortality or 30-day all-cause readmissions among patients presenting to the ED with AHF. KEY WORDS: Emergency department, Heart failure, Lactate, Albumin, Mortality.