Our study showed a high prevalence of OSA among strokevictims (55%), which is consistent with the abundant data inthe literature [8, 9]. More importantly, it demonstrated theprevalence to be clustered in the WUS stroke population(OR 3.25) which is indicative that the main hazard of OSAfor ischemic stroke is mainly during sleep. Numerous reportshave examined the stroke mechanism commonly implicatedin patients with OSA. Cardiac emboli have been repeatedlyshown to be a common source of stroke in the patients withunderlying OSA. In fact, two cardiac lesions have been iden-tified as the culprit for this increase in cardiac source of emboli in this patient population. One is through atrial fibrillation which has already been established as the most common car-diac source of stroke. Cardiac emboli, from atrial fibrillation,have been consistently demonstrated as a frequent source ofstroke in the patients with underlying OSA [21]. Patent fora-men ovale, through paradoxical emboli, is another commonmechanism for cardio-embolic stroke during sleep. Patentforemen ovale is quite prevalent in the general population.However, when it occurs with OSA, it significantly increasesthe risk of cardiac emboli in the patients whose stroke occursduring sleep [22, 23].