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Figure 4 (A) Electrograms during vagal excitation in a patient with chronic atrial fibrillation (AF). Blue and red arrows highlight the atrial activity. (B) Cycle length in the coronary sinus (CS) and pulmonary vein (PV) during the same episode displayed in (A). Mean cycle length in the PV decreased from 156 ms to 144 ms during atrioventricular block. Note that changes in cycle length are smaller than in a patient with paroxysmal AF (Fig. 3).