BACKGROUND: Patients with chronic heart failure (heart failure) are at risk of thromboembolic events, including stroke, pulmonary embolism and peripheral arterial embolism, whilst coronary ischaemic events also contribute to the progression of heart failure. Long-term oral anticoagulation is established in certain groups, including patients with heart failure and atrial fibrillation but there is wide variation in the indications and use of oral anticoagulation in the broader heart failure population. OBJECTIVES: To determine whether long-term oral anticoagulation reduces total deaths and/or major thromboembolic events in patients with heart failure, when compared to placebo. SEARCH STRATEGY: Reference lists of papers resulting from this search, electronic database searching (MEDLINE, EMBASE, DARE), and abstracts from national and international cardiovascular meetings were studied to identify unpublished studies. Relevant authors of these studies were contacted to obtain further data. SELECTION CRITERIA: Randomised controlled trials (RCTs) comparing oral anticoagulants with control or placebo. Non-randomised studies were included as they may help in assessing side-effects. Duration of treatment at least 1 month, adults with heart failure due to any underlying cause. Inclusion decisions were duplicated, disagreement resolved by discussion or a third party. DATA COLLECTION AND ANALYSIS: Data were collected by two reviewers independently and where appropriate data from RCTs were meta-analysed. MAIN RESULTS: One recent pilot RCT compared warfarin, aspirin and no antithrombotic therapy, but no definitive data have yet been published. Three small prospective studies of warfarin in heart failure were also identified, but were over 50 years old with methods not considered reliable by modern standards. Anticoagulation was more efficacious than control for the reduction of all cause death (odds ratio 0.64 95% CI 0.45,0.90) and the reduction of cardiovascular events (0.26 95% CI 0.16, 0.43). Four retrospective non-randomised cohort analyses and three small observational studies of oral anticoagulation in heart failure included differing populations of heart failure patients and reported contradictory results. REVIEWER'S CONCLUSIONS: Evidence from the RCTs and observational studies found a reduction in mortality and cardiovascular events with anticoagulants compared to control. This evidence needs to be interpreted with caution. Although oral anticoagulation is indicated in certain groups of patients with heart failure (eg atrial fibrillation), the data available does not support its routine use in heart failure patients who remain in sinus rhythm. A large randomised trial of warfarin in heart failure patients in sinus rhythm is currently in progress data from which will be useful addition to this story.