[The AV node - an enigmatic »black box« located in the centre of the heart]

This commentary refers to a case report describing dual ventricular responses following a single P-wave, which is an unusual but possibly underdiagnosed phenomenon. The AV node synchronizes atrial and ventricular mechanical functions, acts as an electrical filter protecting the ventricles from high heart rates during atrial fibrillation and flutter and is also a back-up generator if the sinus node fails. Dual AV-nodal pathways are the substrate for the relatively common AV-nodal re-entrant tachycardia (AVNRT), which is curable by ablation. Ablation is also the therapy of choice when dual ventricular responses cause palpitations with or without AVNRT, or in rare cases of continuously impaired ventricular mechanical function.