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The risks and benefits of anticoagulation for patients with both heart failure and atrial fibrillation are unclear. We hypothesized that anticoagulation was associated with improved clinical outcomes of heart failure patients with atrial fibrillation independent of other risk factors. We conducted a retrospective cohort study of clinical registry data linked to Medicare claims for new users of oral anticoagulation (warfarin) without contraindications, discharged home alive, and stratified by CHADS2 score. Outcomes of interest were propensity score-adjusted estimates of the effects of warfarin at discharge on all-cause mortality, thromboembolic events, major adverse cardiovascular events, and bleeding events. Among 10,494 patients with heart failure and atrial fibrillation, the 2249 patients newly treated with warfarin had lower 1-year mortality (27.7% vs 39.3% for CHADS2 score ≤ 3 [P < .001]; 31.6% vs 41.8% for CHADS2 score > 3 [P < .001]) than patients not treated with warfarin. There was no significant difference in thromboembolic events, major adverse cardiovascular events, or bleeding events at 1 year. After multivariate adjustment, exposed individuals in both CHADS2 subgroups had lower adjusted 1-year mortality (CHADS2 ≤ 3: hazard ratio, 0.78 [95% confidence interval, 0.69-0.89]; CHADS 2 > 3: 0.78 [0.66-0.93]). In conclusion, warfarin use in heart failure patients with atrial fibrillation was associated with improved survival at 1 year independent of baseline CHADS2 score. However, there was no significant reduction in clinical events, such as thromboembolic or major adverse cardiovascular events at 1 year that might simply explain the survival benefit associated with warfarin.