Supraventricular tachycardias arise in or involve at least some part of the atrium or atrioventricular junction. Supraventricular tachycardias develop as a result of abnormal automaticity, triggered activity or, most commonly, reentry. Both atrial flutter and atrial fibrillation are supraventricular tachycardias; however, because of the differences in their mechanisms and clinical manifestations, they are grouped separately from other types of supraventricular tachycardias, commonly referred to as paroxysmal supraventricular tachycardia (PSVT).