Supraventricular tachycardias (SVTs) affect all age groups and are a source of significant morbidity. They are frequently encountered in otherwise healthy individuals without structural heart disease. Advances in the understanding of their mechanisms and anatomical locations have led to highly effective pharmacologic and nonpharmacologic treatment strategies. Recognition, identification, and differentiation of the various SVTs are of great importance in formulating an effective treatment strategy. Developments over the past four decades have made possible the accurate diagnosis of SVTs. Today, advances in catheter design, energy delivery systems, mapping systems, and remote navigation systems have rendered the ablation of most SVTs safe and effective. This monograph provides an in-depth discussion of the history, presentation, mechanism, and treatment strategies of the most commonly encountered SVTs. The monograph is divided into two parts. The first part is presented here.