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Figure 4 Pulmonary vein flow from the animal in Figures 2 and 3, again at baseline (top left panel), and after one week of rapid atrial pacing at 400 beats/min (bottom left panel), two weeks of rapid ventricular pacing at 220 beats/min (top right panel), and both rapid atrial and ventricular pacing (bottom right panel). Recordings were obtained during atrioventricular sequential pacing at 80 beats/min. J1 = early systolic flow; J2 = late systolic flow; K = diastolic flow. A prominent atrial reversal wave (A) is seen after rapid ventricular pacing. Doppler scale = 20 cm/s. Diastolic reversals in the lower two panels occur during isovolumic ventricular systole and are not pulmonary vein A velocities. See text for details.