Background: Atrial septal defect (ASD) is a common congenital heart disease in adults. Concomitant mitral valve disease in patients with ASD could have significant hemodynamic effects whit a great impact on managing this congenital defect. Objectives: This study evaluated the prevalence of mitral valve abnormalities and the hemodynamic burden associated with different types of ASD. Methods: This retrospective study reanalyzed 1,006 consecutive patients referred to Rajaie Heart Center in Tehran from March 2019 to February 2022. We evaluated adult patients with the diagnosis of a shunt at the atrial level. Diagnoses were made with 2D and 3D transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE). 3D analysis was performed with 3D zoom, mitral valve navigation (MVN), and full-volume and multi-planar reconstruction (MPR) modalities. We performed statistical analysis by SPSS version 22.0. The qualitative data were expressed as frequency and percentage. Data were compared between subgroups via Mann-Whitney U/Kruskal-Wallis tests for the interval variables, Pearson's chi-square test for nominal variables, and chi-square for trends test for ordinal variables. Results: The distribution of different ASD types was ostium secundum in 88.8% of cases, primum ASD in 0.9%, SVC-type sinus venosus ASD in 9%, IVC-type sinus venosus in 0.4%, and unroofed coronary sinus in 0.9%. We found mitral valve abnormalities in 21.1% of cases, and the most common mitral valve abnormality were prolaptic lesions (17.4%). Conclusions: Age, ASD size, estimated Systolic Pulmonary Artery Pressure (SPAP), and severity of mitral regurgitation (MR) were markedly higher were markedly higher among patients with MV anomalies, more over left ventricular ejection fraction (LVEF) was significantly lower among this group (P-value < 0.05).