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Figure 7 Right panel illustrates the activation map of section 3 of the penultimate bigeminal beat (A) and the last bigeminal beat that initiated ventricular tachyarrhythmia (B) from the experiment shown in Figure 6. Isochrones of activation are drawn at 20-ms intervals and labeled 1, 2, 3 and so on, and functional conduction block is represented by heavy solid lines. Left panel illustrates electrograms from selected sites on the two maps (A1 to A4 and B1 to B4). The electrograms labeled A* and B* were recorded at the site of origin of bigeminal beat A and B, respectively. Both beats arose from the same right ventricular subendocardial site in section 2 (not shown in the figure). The numbers in parentheses represent the local activation–recovery intervals (ARI) at each site. Note that the ARIs of B1 to B4 were 19 to 37 ms longer compared with A1 to A4. Functional conduction developed between sites B3 and B4 because of increased dispersion of repolarization (DR).