Our objective was to create a simple prognostic risk score for patients with systolic heart failure and mild symptoms. We then assessed the efficacy of eplerenone across different categories of risk. Methods and results The Eplerenone in Mild Patients Hospitalization and Survival Study in Heart Failure trial (EMPHASIS-HF) was an international randomized trial, comparing eplerenone with placebo in 2737 patients with systolic heart failure and mild symptoms. The primary outcome was a composite of cardiovascular death or hospitalization for heart failure, over a median 2.1 years follow-up. Using multivariable Cox modelling age, sex, systolic blood pressure, estimated glomerular filtration rate, diabetes, BMI, haemoglobin, prior heart failure (HF) hospitalization, prior myocardial infarction/coronary artery bypass surgery (CABG), and heart rate were identified as strong independent risk factors. Estimates from the model were converted into a simple integer risk score which was categorized into three groups of low-, medium-, and high risk. In placebo patients, the rates (per 100 patient-years) for the primary outcome were 7.6, 19.0, and 39.4 in the low-, medium-, and high-risk groups, respectively. On eplerenone, these rates were reduced to 5.6, 12.2, and 24.2, respectively. Eplerenone was beneficial across all risk categories and the hazard ratios were similar. The absolute treatment benefit was greatest among those at highest risk. Similar patterns emerged for all-cause mortality and for all HF hospitalizations. Conclusion This easy-to-use integer risk score should be of value in quantifying individual patient risk in patients with systolic HF and mild symptoms. The relative benefits of eplerenone appeared consistent across the whole spectrum of risk, including those at lower risk.