Objective: Diagnostic and interventional cardiac catheterization procedures for congenital heart diseases (CHD) are becoming increasingly more popular, and arrhythmia is a well-knowncomplication. This study was an evaluation of the incidence andcausative agents of arrhythmia and the subsequent treatmentstrategies applied during cardiac catheterization.Methods: The catheterization data of all of the patients whounderwent diagnostic cardiac catheterization for CHD between January 2012 and 2018 at a single center were examined retrospectively.Results: A total of 1316 children underwent diagnostic cardiaccatheterization due to CHD. The median age and body weightwas 18 months (6 days-21 years) and 9.9 kg (2.2–135 kg), respectively. Patients with ventricular septal defect (281 patients)and those with tetralogy of Fallot (257 patients) represented2 major groups of the study population. In 93 (7%) patients,arrhythmia developed during cardiac catheterization. Amongthem, there were 58 (62%) cases of bradyarrhythmia and 35(38%) cases of tachyarrhythmia. Arrhythmia was classified aslow, high, or major, according to the adverse event severityscore; the rates were 2.7%, 4.3%, and 1.2%, respectively. In36 (39%) patients, there was no need for therapy, whereas 57(61%) required treatment to eliminate the arrhythmia. Treatment modalities included catheter manipulation in 15, pharmacological therapy in 24, and cardioversion in 3 patients. Elevenpatients required cardiopulmonary resuscitation. Temporarypacemaker implantation was required in 2 patients, while 2 others underwent permanent pacemaker implantation secondaryto catheterization-related arrhythmia. There were no cases ofmortality secondary to catheterization-related arrhythmia.Conclusion: Diagnostic cardiac catheterization in CHD mayresult in various types of cardiac arrhythmias. The propermanagement of arrhythmias may reduce morbidity and mortality related to cardiac catheterization.