Background: Arrhythmias occur often in the early postoperative period, where hemodynamic variations are normal, rendering the patient unstable and can lead to low c ardiac output and cardiac arrest unless treated and resolved in a timely manner. The aim of this study was to analyze the possible causes and risk factors of early arrhythmias to determine the outcome of patients and prevention of arrhythmias after congenital cardiac surgery in pediatrics. Methods: This Prospective observational study was conducted in the pediatric cardiothoracic intensive care unit (ICU) and pediatric cardiology unit of Zagazig university, the target sample included 24 patients <18-years of both sexes who underwent cardiac operation with or without cardiopulmonary bypass (CPB) between January to July 2020. All patients underwent echocardiographic examination before and after surgery. Children were monitored in the early postoperative period (72h) for the detection of any rhythm abnormality and followed until they were discharged from hospital. Results: This study showed that early arrhythmias occurred after open heart surgery and all presented in the first 72 hours. The most common type of arrhythmias encountered in this study were JET (12.5%) in three cases diagnosed as ASD, VSD and TOF , SVT (4.2%) in one case of PDA+VSD.electrolyte disturbance one of causes of increase chance of arrhythmias occurrence in postoperative period in our study. Conclusions: Early Postoperative arrhythmias are still a frequent complication in the early period of congenital cardiac surgery in pediatric patients, especially junctional ectopic tachycardia. Hemodynamically significant arrhythmia could be lethal in patients with severe underlying heart diseases.