Cerebral ischemia is among the principal causes of mortality and morbidity in industrialized countries being responsible of 10-12% of all deaths and of an elevated number of permanent disability. The cardio-embolic forms may be responsible of the 30-35% of cerebrovascular acute syndrome, nevertheless in a significant percentage of cases, especially among young people, cerebral ischemic episodes are not induced by these cardio-embolic forms: these cases are defined as cryptogenetic stroke/TIA. In these patients cardiac abnormalities represented by an aneurysm of the interatrial septum (ASA) and by a patent foramen ovale (PFO) have been frequently observed. The purpose of our prospective, study was to evaluate, through transthoracic echocardiography and tissue harmonic imaging (ETT-THI), the prevalence of ASA in the general population (group A) and the prevalence of ASA-FOP in a subgroup of patients with recent episode of cryptogenetic ischemic stroke/TIA (group B). We studied in a prospective manner from January 1 2003 to October 31t 2004 n. 5.631 patients. The presence of ASA was found in 3.2% of patients of group A, while in patients of group B we identified an ASA in 32% and a POF in 42% of the cases. Using a ETT-THI, our study shows in a wide range of a non selected population a prevalence of ASA greater than in previous studies. Such high prevalence in the general population of patients submitted to echocardiography and the higher frequency in subjects with recent cryptogenetic stroke, suggests to search carefully these abnormalities at the level of the interatrial septum using the harmonic imaging method.