AIMS: It is not known whether concomitant use of aspirin might attenuate the beneficial effects of mineralocorticoid receptor antagonists (MRAs). The purpose of this subgroup analysis was to explore the interaction between baseline aspirin treatment and the effect of eplerenone on the primary efficacy outcomes (composite of hospitalization for heart failure or cardiovascular mortality), its components, and safety markers [estimated glomerular filtration rate (eGFR), systolic blood pressure (SBP), and serum potassium >5.5 mmol/L] in the Eplerenone in Mild Patients Hospitalization and SurvIval Study in Heart Failure trial (EMPHASIS-HF). METHODS AND RESULTS: Patients with chronic heart failure, reduced ejection fraction (HFREF), and mild symptoms were enrolled in EMPHASIS-HF. We evaluated baseline characteristics according to aspirin use. We explored the interaction between aspirin and eplerenone, using Cox proportional hazards models providing adjusted hazard ratios (HRs) with 95% confidence intervals (CIs) and P-values for interaction. Of the 2737 patients randomized, 1605 patients (58.6%) were taking aspirin. The beneficial effects of eplerenone on the primary endpoint were similar in patients not treated (adjusted HR 0.59, 95% CI 0.46-0.75) or treated (adjusted HR 0.71, 95% CI 0.59-0.87) with aspirin at baseline (interaction P-value = 0.19). We did not observe any significant modification of the safety markers by aspirin that was clinically meaningful. CONCLUSION: Aspirin use in patients with chronic systolic heart failure and mild symptoms did not substantially reduce the overall beneficial effects of the MRA eplerenone contrary to what has been described in some studies with ACE inhibitors.