Stroke is one of the leading causes behind death and permanent disability in adults. Atrial fibrillation (AF) is the most common clinical arrhythmia and its prevalence is steeply increasing with age. Atrial fibrillation is associated with a manifold increase in the risk for stroke. It is considered important to investigate the heart rhythm in stroke survivors without previously known AF, because detection of AF will prompt a change in antithrombotic treatment with subsequent lowering of the risk of recurrent stroke. There are so far very few studies on the prognostic impact of ECG investigations post stroke. Despite this knowledge gap, ECG investigation post stroke is given high priority in national and international guidelines. Considerable clinical resources are currently invested in these ECG investigations without knowledge of its utility. The investigators plan a nationwide, randomised, register-based study (RRCT) including patients aged at least 70 years receiving in-hospital care for stroke or TIA (Transient Ischemic Attack). Included patients will be randomised to standard investigation (1-2 days of ECG ) or extended ECG investigation (14 days of ECG performed at least twice). Patients diagnosed AF will be offered anticoagulation treatment. Long-term follow-up will be performed via swedish health care registers. The result of this trial will have major impact on the ECG screening recommendations for patients who have had stroke, a large group of patients with dismal prognosis.