Narrow QRS complex tachycardias originating from the atrioventricular (AV) node region primarily include atrioventricular nodal reentrant tachycardia (AVNRT) and junctional ectopic tachycardia (JET). While AVNRT, the most common paroxysmal supraventricular tachycardia, is based on a reentrant mechanism involving dual AV nodal physiology, JET predominantly arises from enhanced automaticity or triggered activity and frequently occurs either congenitally or postoperatively. Electrophysiological studies allow for a differentiated diagnosis of both entities, with maneuvers such as ventricular stimulation and analysis of retrograde activation patterns being particularly helpful in distinguishing AVNRT from other supraventricular tachycardias. In terms of therapy, modified vagal maneuvers, adenosine, and especially catheter ablation in long-term management are central for AVNRT, whereas in JET, pharmacological therapy, treatment of underlying causes, and ablation in selected cases are employed. A thorough understanding of the anatomical and electrophysiological foundations is essential for targeted diagnosis and therapy of these tachycardias.