Abstract: Iatrogenic atrial septal defect (IASD), post Catheter ablation during electrophysiological study simply can be assess with Echocardiography nowadays ablation consider the main line in the managements of patients with various type of arrhythmia. This study aims to determine the outcomes of Iatrogenic Atrial Septal Defect (IASD) six months post radiofrequency ablation (RF) procedure of left atrial arrhythmia using non-invasive Transthoracic Echocardiography (TTE) parameters (LVEF, E/e` and ASD size) with sheath size as predictors of atrial septal defect closure. Patients and methods: A prospective study was conducted in Iraqi Centre for Heart Diseases included 47 patients post Electrophysiology procedure and ablation of left atrial SVT were selected after non complicated transeptal puncture using two size of sheath in three type of arrythmia and follow up done simply with Transthoracic echocardiography (TTE) was used to evaluate the atrial septal defect (ASD) (from May 2019-May 2020) in Iraqi centre for heart diseases, Results: After Electrophysiology study, results of this study were analysed and collected according to duration of procedure, sheath size and number that used in septostomy, size of IASD and Echocardiographic parameters. The mean age of the patients (36.28±10.34 years), males were 23 (48.9%) while females were 24 (51.1%), without structural heart diseases and good LV function with mean EF (64.68± 5.23%) . Iatrogenic atrial septal defects (IASDs)were detected by TTE in all patients with range from (2-5) mm with mean of (3.47±0.92), performed by Transseptal puncture (TSP), either with single 8 French sheath in 24 (51.06%) patients or single 12 French sheath in 17 (36.17%) patients while 6 (12.77%) patients the defect was performed by double transseptal sheath. spontaneous closure occur in 35(74%) patients within first three months with clear significant association between size of ASD that related to the sheath size and duration of procedure (P<0.0001). We notice that some Echocardiographic parameters were also associated with IASD without any clinical complications and/ or deterioration. Conclusions: post catheter ablation number and size of sheath and duration of ablation consider as a predictor to closure of residual atrial septal defect post atrial septostomy and can simply assess with non-invasive Transthoracic Echocardiography parameters such (Atrial septal defect size and body surface area) during initial six months follow up.