Although paradoxical brain embolism result in the right-to-left shunt (RLS) is very important etiology of ischemic stroke especially in young adults, the detailed characteristics of them in Japan remain unknown. In collected clinical data for 7,245 acute stroke patients, patent foramen ovale (PFO) were more frequent in the young patients group (n = 1,584) than in the non-young patients group (n = 5,661) (0.7% vs. 1.2%, p = 0. 07). The frequency of PFO was rare than that of previously reported. Suspected reason is that the limited patients were underwent transesophageal echocardiography (TEE). The golden standard to detect RLS is contrast-enhanced TEE, and standardization of procedure is the most important factor. In our hospital, positive rate of RLS was risen up to 21.9% from 8.8% by standardization. In the patients with RLS in our hospital, the definite and probable criteria of paradoxical brain embolism were fulfilled only in 7.7% and 38.5%, respectively. If patients have any other risk factors (e.g. venous thrombus, cardiac source of embolism), to prevent recurrent stroke associated with RLS they must be underwent anticoagulation and correctly controlled by PT-INR. And if patients have no other risk factors, PICCS study confirmed that there was no difference of recurrence rate between anticoagulation and aspirin therapy.