Background: Corticosteroid therapy is widely used in pediatrics in many inflammatory and autoimmune disorders.Reports have documented various cardiovascular disorders and arrhythmias occurring during corticosteroid pulse therapy. This study aimed to assess the impact of high-dose intravenous methylprednisolone on indices of ventricular repolarization in children at Benha University Hospitals. Methods: This observational study included 50 children (30 males, 20 females; mean age 7.1 ± 4.5 years) who received pulse steroid therapy,dose of pulse steroid therapy 10-30mg/kg for 3-5days with max dose 1gram/d.Each underwent full clinical evaluation, laboratory investigations, and ECG monitoring 4 hours before and 12 hours after methylprednisolone infusion. Results: The most common indications for therapy were nephrotic syndrome (16%), ADEM (10%), GBS (8%), and autoimmune hemolytic anemia (8%). ECG parameters including heart rate (HR), corrected QT interval (cQT), Tpeak-Tend interval (Tp-e), and Tp-e/QTc ratio significantly increased post-therapy, while PR interval significantly decreased (p < 0.05). No significant changes were noted in QRS or JTc. Adverse effects were reported in 46% of patients: fatigue & weakness (18%), headache (22%), irritability (6%), blurred vision (4%), sleep disturbance (10%), GIT irritation (14%), hotness (6%), and palpitation (10%). All patients survived, with no arrhythmias,86% responding to steroid therapy alone, while 14% required IVIG. The average hospital stay was 14.2 ± 3.9 days. Conclusion: High-dose intravenous methylprednisolone significantly alters ventricular repolarization markers, indicating a potential risk of arrhythmia in pediatric patients. ECG monitoring is essential during therapy. Identifying at-risk patients early and ensuring careful follow-up can minimize adverse cardiac events.