Background: of all the types of congenital heart disease, ASDs represent the second most common and account for 7% to 10% of all congenital heart defects. The most common type of atrial septal communication is an ostium secundum defect, representing 80% of all ASDs. In unaffected individuals, the chambers of the left side of the heart are under higher pressure than the chambers of the right side. In the case of ASD, which may result in a clinically remarkable left-to-right shunt, blood shunts from the left atrium to the right atrium. This extra blood from the left atrium may cause a volume overload of the right side. Aim of the Work: The aim of this work was to assess feasibility of using 2-dimensional speckletracking echocardiography (2D-STE) for evaluation of left and right atrial function in patients with unrepaired atrial septal defect, to compare both LA & RA function in patients with unrepaired atrial septal defect with those apparently healthy individuals, and to correlate both LA & RA function with the size of inter-atrial shunting. Patients and Methods: The ethical approval was obtained from the hospital Ethical Research Committee and each patient entering the study signed an informed consent. Thirty patients included in this study with secundum atrial septal defect. All were under the age of sixteen at time of diagnosis. They were recruited from cardiovascular department at Sayed Galal University Hospitals during the period from December 2016 to November 2018. Results: Speckle tracking echo of both atria showed a significant correlation with QP/QS, ASD maximal size, ASD minimal size, RA to LA area ratio and pulmonary pressure. Patients with PH were older (33.4+/-14.6 vs. 23.8 +/- 12.2 years; p<0.06) and had larger defects (17.8+/4.6 mm vs. 14.5.1+/- 5.0 mm; p<0.08). The proportion of women was nearly similar in both groups (55% in patients with PH vs. 63% in those without; p=NS). Most patients with PH had ASDs with more complex shapes on echocardiography. However, some patients with simpler and smaller defects, such as central ASD with a diameter of <5 mm, also developed PH. Conclusion: The new echocardiographically-derived myocardial deformation indexes, which reflect structural changes assessed by transthoracic echocardiography, can be used to detect abnormalities in atrial function before clinical deterioration