 Stroke remains the most dangerous and frightening complication of atrial fibrillation AF. Numerous factors predisposing to peripheral embolism in patients with AF have been well defined, documented and included in the CHA2DS2VASC score. Although proper anticoagulation minimizes the risk attributable to known risk factors, stroke may still occur. Thus, unknown risk factors may play an important role in stroke risk stratification in patients with AF. The investigators assume that one of the important unknown risk factor is left atrial appendage LAA morphology. The ASSAM study is planned to include 100 patients after ischemic stroke or transient ischemic attack TIA and known status of anticoagulation at the time of stroke. The control group will consist of 100 patients scheduled for AF ablation without a history of stroke or TIA. 