In this article, the authors discuss the features and differential diagnosis of supraventricular tachycardia with a regular ventricular rate that occurs in patients without overt preexcitation during sinus rhythm. In the authors' experience, the two most common mechanisms of these tachycardias are reentry within the atrioventricular node (AV nodal reentry) and atrioventricular reentry using a concealed accessory pathway for retrograde conduction and the AV node/His-Purkinje system for antegrade conduction (AV reentry). Sinus nodal reentry, intra-atrial reentry, automatic atrial tachycardia, and nonparoxysmal junctional tachycardia account for the remaining episodes of regular supraventricular tachycardia. Therapy for AV and AV nodal reentry is also discussed.