Atrial fibrillation is associated with increased risk of thromboembolism, as illustrated by an increased incidence of stroke and thromboembolic events. Hemostatic abnormalities have been demonstrated in patients with atrial fibrillation in numerous studies, with increased markers of coagulation and fibrinolysis, and altered levels of plasma markers of platelet and endothelial origin have been reported. Nevertheless, the mechanism by which atrial fibrillation causes these abnormalities has yet to be fully elucidated. In order to reduce risk of thromboembolism in atrial fibrillation, anticoagulant and antithrombotic therapies have been assessed in randomized control trials, with dose-adjusted warfarin showing a clear reduction in stroke rate in “at-risk patients” on metaanalysis. However, stroke risk in atrial fibrillation is heterogeneous, and, currently, risk stratification on clinical grounds is used to decide the best therapeutic strategy in individual patients...