The 2006 American Heart Association / American Stroke Association Council on Stroke Guidelines for Prevention of Stroke in Patients With Ischemic Stroke or Transient Ischemic recommended that patients with cryptogenic stroke take antithrombotic drugs (i.e. aspirin) in order to prevent a second stroke. When a stroke patient is found to have atrial fibrillation (AF), the guidelines recommend oral anticoagulation due to its superior efficacy over aspirin for stroke prevention. Physicians can best optimize the use of medicines only if they can precisely and correctly diagnose a patient's AF. The purpose of this study is to evaluate the time to first AF by 6 months' continuous rhythm monitoring versus control treatment in subjects with a recent cryptogenic stroke or Transient Ischemic Attack (TIA) without history of AF.