Variations and delays in the diagnostic procedures during hospitalization after acute ischemic stroke are still common, and at the same time, stroke aetiology remains cryptogenic in about 20-25% of stroke unit patients. Recent studies have shown that (a) cardiac MRI is now able to detect cardiac sources of embolism (thrombi and aortic plaques) with equal sensitivity as compared to echocardiography, and (b) prolonged ECG monitoring up to several days/weeks/years can significantly increase the detection rate of atrial fibrillation. These developments might allow a faster and more effective diagnostic work-up in patients with acute ischemic stroke compared to standard diagnostic procedures including doppler-ultrasound of the extracranial brain-supplying arteries, echocardiography, 24-h-Holter ECG and stroke unit monitoring. This prospective observational trial therefore aims to assess the detection rate of pathologic findings relevant to stroke aetiology as obtained by an enhanced MRI set-up (including cardiac MRI, MR-angiography of the brain-supplying arteries) and a prolonged Holter-ECG (of up to 5 days after the stroke) in comparison to findings obtained by routine diagnostic procedures after acute stroke.