Preexcitation syndromes are a common cause of paroxysmal tachycardias presenting to the ED. Emergency physicians should be familiar with the common electrocardiographic manifestations of preexcitation, particularly the Wolff-Parkinson-White abnormality, as these conditions require specific therapeutic management. This article reviews the pathophysiology of preexcitation, along with the electrocardiographic findings of Wolff-Parkinson-White and its associated tachyarrhythmias.