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An 83-year-old man was evaluated for frequent palpitations. During an episode, examination of the neck revealed rapid and regular pulsations with bulging of the internal jugular veins .A 12-lead electrocardiogram was obtained and showed a regular, narrow-complex tachycardia, with narrow P waves deforming the terminal QRS complex (Panel A, arrowheads). The P wave is negative in the inferior leads (forming a pseudo-S wave) and positive in lead V1 (forming a pseudo-r′ wave). On the application of pressure to the carotid sinus, the tachycardia and the bulging of the internal jugular veins were resolved .and sinus rhythm was restored. The characteristics of the arrhythmia were suggestive of atrioventricular nodal reentrant tachycardia, a functional reentrant arrhythmia localized to the AV junction. In its typical form, anterograde conduction occurs over the slow pathway to the ventricle, while near-simultaneous atrial activation occurs over the fast pathway of the AV node. These events lead to the parallel electrical activation of the atria and ventricles. Canon A waves result from the simultaneous contraction of the atria and ventricles against closed atrioventricular valves, causing a reflux of blood into the neck veins.