Introduction: the interatrial septum defects are frequent. A new entity has recently been identified, known as septal pouch. Prevalence data in general population is scarce, and is estimated between 30%-50%. The role as a source of cardioembolism is unclear.Objectives: the primary objective is to determine the prevalence and characterize the septal pouch; secondarily to define the interobserver variability for the diagnosis.Material and methods: observational, descriptive and analytical study. Consecutive patients were recruited for transesophageal echocardiography between 4/20/2018 and 8/30/2018. Werecorded patronymic data, personal history of stroke, heart rate, and the reason for the study. The presence of septal pouch was defined and characterized as left-sided septal pouch or rigth-sided septal pouch; depth was measured, presence of thrombus inside and echocardiographic study measures were completed. The images were evaluated by two blind echocardiographers. The qualitative variables are presented in relative frequency (RF), the quantitative variables in median and interquartile interval. Chi square test was carried out. The reproducibility of the diagnosis of septal pouch was evaluated by Kappa index.Results: 50 subjects were included. The prevalence of septal pouch was 0.5 (RF), 0.46 left-sided septal pouch and 0.04 rigth-sided septal pouch. The interobserver Kappa index for diagnosis is 0.68, standard error 0.14, with 84% agreement. 14 subjects had stroke, in 9 of them septal pouch was diagnosed (chi square p=0.21); 18 patients had atrial fibrillation or flutter, half of them had septal pouch (chi square p=1).Conclusion: the prevalence of septal pouch was half of the population, predominantly the left-sided septal pouch, with good reproducibility in diagnosis. It is an underdiagnosed finding; further investigation is necessary to assess its relation to stroke.