Background: The risk of thromboembolism in chronic heart failure and the risk-to-benefit ratio of anticoagulation in this population are poorly defined. Methods and Results: A PubMed/MEDLINE search of published trials was performed. Twenty-four studies were identified after exclusion of individual case reports. All studies were prospective or retrospective observational reports, either independent studies or secondary analyses of prospective clinical trials in patients with heart failure. Prevalence estimates ranged of thromboemboli ranged from 3% to 50% and incidence estimates ranged from 1.5 to 3.5/100 patient-years. Although no randomized data of therapeutic anticoagulation were identified, a secondary analysis of one study suggested event reduction in patients receiving warfarin anticoagulation; other studies failed to suggest such benefit. Overall bleeding estimates in warfarin-treated patients ranged from 2.3 to 6.8/100 patient-years. Intracranial hemorrhage rates were 0.62 to 0.9/100 patient-years but increased with age. Only one study suggested that aspirin was beneficial in reducing clinically significant emboli. Conclusions: Although patients with chronic heart failure and left ventricular dilation have a higher risk of thromboembolism, data are insufficient to recommend warfarin or aspirin prophylaxis in the absence of additional indications for such therapy.