Background: Knowledge of the size, location and type of the atrial septal defect is very important guideline for clinicians to decide the type of intervention required .The objective of the study was to determine the same using transthoracic echocardiography. Method: Total 42 patients diagnosed with atrial septal defect were studied using twodimensional echocardiography. Examination was done by Siemens ultrasound echo machine using a P5-1MHz transducer.