The ability to diagnose basic arrhythmias and conduction disorders in infants, children, adolescents, and adults with congenital heart disease is a fundamental of pediatric and adult congenital cardiovascular medicine. This chapter provides basic knowledge regarding the physiology of cardiac conduction, practical information on the diagnosis of common rhythm disturbances, and general instruction on the primary methods for acquisition of electrocardiographic data, including body surface electrocardiography, ambulatory monitoring, and provocative electrophysiology study. The knowledge obtained from this chapter will form a foundation for further understanding rhythm disturbances in even the most complex patients with congenital heart disease.