Inclusion criteria  Acute ischemic stroke defined as an acute episode of neurological dysfunction caused by focal cerebral infarction and/or a corresponding lesion on brain imaging Stroke symptoms within 7 days Age ≥ 50 years At least one 12-lead ECG has already been obtained as part of the routine clinical workup after admisison, and no ECGs have shown any episodes of atrial fibrillation or atrial flutter  Exclusion criteria  History of atrial ﬁbrillation/atrial flutter or documented atrial ﬁbrillation/atrial flutter prior to enrollment Intracerebral hemorrhage in medical history Implanted pacemaker device or cardioverter/deﬁbrillator End stage renal disease Endocarditis Untreated hyperthyroidism Myocardial infarction or cardiac surgery less than one month prior to index stroke Any finding on echocardiography for which there is already an evidence-based indication for long-term anticoagulation (e.g. mechanical heart valve, thrombus, etc.)