Abstract Objectives: Cardiac manifestations of the coronavirus disease 2019 (COVID-19) have mainly been reported in adults. Therefore, we aimed to determine the electrocardiographic abnormalities in hospitalised paediatric patients with COVID-19 and multisystemic inflammatory syndrome in children. Methods: We retrospectively evaluated hospitalised paediatric patients <18 years of age with a diagnosis of COVID-19 (n = 168) and multisystem inflammatory syndrome in children (n = 48) between March 2021 and December 2021. A daily electrocardiography was performed for the patients who had electrocardiographic abnormalities on admission or developed electrocardiographic abnormality on the follow-up. The characteristics of these patients, underlying predisposing conditions, and clinical course were also examined. Results: Two-hundred sixteen paediatric patients (55% were male) with a mean age of 10.7 ± 4.69 years were evaluated. There was an underlying disease in 84 (38.8%) patients and 51 (23.6%) required paediatric ICU admission. Electrocardiography abnormality was detected in 12 (5.5%) which were as follows: 7 (3.2%) had sinus bradycardia, 3 (1.4%) patients had transient ST elevation and concomitant T negativity, and 2 (0.9%) developed first-degree Atrioventricular (AV) block. The median time from the onset of disease symptoms to detecting electrocardiographic abnormality was 9 days. Electrocardiographic abnormalities returned to normal uneventfully 3 days later. Conclusions: The prevalence of arrhythmia in paediatric patients with COVID-19 was detected in 5.5% of the patients. While two-thirds of the electrocardiography abnormalities were sinus bradycardia, ST elevation was remarkable (1.4%). Clinicians should be aware of electrocardiographic abnormalities and consider electrocardiographic monitoring in paediatric patients with COVID-19 and multisystemic inflammatory syndrome in children.