This study will (1) evaluate whether a gene marker can improve the identification of AF in patients with ischemic stroke, and (2) evaluate decisions by health care provider and patients to anticoagulate AF, and whether this decision could be improved by a marker of AF at time of stroke. An AF Gene Score will be developed comprised of genes associated with inflammatory and thrombotic pathways related to risk of AF thromboembolism in stroke patients with AF. The AF Gene Score measured at time of stroke can stroke will permits rapid identification of stroke due to AF which may increase initiation of anticoagulation therapy. This is important in cryptogenic stroke, where prolonged monitoring leaves uncertainty regarding the association of delayed AF with initial stroke and delays anticoagulation.