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Figure 3 Cardiac nerve stimulation in the CS. Surface ECG lead II, aVR and an RAA recording are depicted. Atrial fibrillation was induced and maintained by rapid pacing from the RAA at a cycle length of 100 ms (low frequency, low amplitude pacing artifacts on the right of the RAA tracing). Parasympathetic stimulation was done at a stimulus strength of 34 V and a frequency of 20 Hz (high frequency, high amplitude electrical artifacts can be seen on the left of the RAA tracing). The cycle length values within the figure refer to the longest and shortest R-R interval during AF with PS (1976 and 1440 ms, respectively) and when PS was terminated (arrow, 600 and 260 ms, respectively). AF = atrial fibrillation; CS = coronary sinus; PS = parasympathetic stimulation; RAA = right atrial appendage; R-R = ventricular rate.