[Atrioventricular nodal reentrant tachycardia with 2:1 anterograde block]

We describe the case of a patient who presented with narrow QRS tachycardia at a rate of 100 b/min. The R-R intervals were constant, and negative P waves were evident in the inferior leads, midway between two ventricular complexes. A few minutes later, the tachycardia rate suddenly increased to 190 b/min, and the electrocardiographic pattern became typical of atrioventricular nodal reentrant tachycardia. Intravenous verapamil succeeded in restoring sinus rhythm. These data suggested an atrioventricular nodal reentrant tachycardia that at the beginning was associated with a 2:1 anterograde block.