Inclusion Criteria:  - Patients who have had a cerebral or retinal infarction confirmed by brain imaging or a defined transient ischemic attack without an identifiable cause after a detailed etiological assessment  Exclusion Criteria:  Identification of a cause of ischemic stroke:  Atheromatous stenosis > 50% (or atherosclerotic plaque < 50% threatening) of supra aortic trunk or intracranial arteries on echodoppler of the supra aortic trunk and transcranial or scanner angiography. Emboligenic heart disease : atrial fibrillation and atrial flutter, thrombus in left atrium, spontaneous contrast in left atrium, decreased atrial flow, left ventricular ejection fraction (LVEF) < 40%, LV aneurysma, left intraventricular thrombus, recent myocardial infarction, cardiomyopathy ventricular dilated left with LVEF < 35%, mitral stenosis, prosthetic mitral or aortic valve, infectious and non-infectious endocarditis, valve or mural tumor, complicated aortic arch atheroma (plaque > = 4 mm, ulcerated plaque, thrombus on plaque), aortic dissection Lacunar infarction symptomatic = < 1.5 cm on the CT scan, = < 2 cm on the diffusion MRI or the FLAIR. No atherosclerotic arteriopathy : dissection, primary and secondary angitis, spastic angiopathy, etc… Coagulopathy to come a long-term anticoagulant treatment (> 6 months) (anti-phospholipid syndrome, thrombophilia). Blood disorders and cancer Recent intravenous drug use (in the 6 months before the stroke). Other potential causes: Severe respiratory impairment or pulmonary arterial hypertension