Arrhythmias are a major cause of morbidity and mortality in adults with congenital heart disease; they can range from occult asymptomatic sinus node disease to sudden death. Detecting and diagnosing these arrhythmias presents a challenge when caring for these patients. A high index of suspicion is necessary, as well as a thorough understanding of the underlying heart defect and subsequent surgical interventions. A careful history, noninvasive evaluation, and in some cases invasive testing are all necessary to determine arrhythmias in this population.