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Figure 4 (A) Regional fractional area change (RFAC) maps for each sector corresponding to the cardiac variability imaging images shown in Figure 3. The location of each segment is identified in the prior figure. In normal sinus rhythm (stimulation off), septal contraction often displayed early negative RFAC followed by late positive deflection (expansion) and lateral contraction showed the opposite pattern. Left ventricular pacing improved motion in the septum toward normal but had minimal effects on lateral wall motion. (B) Mean results for maximal RFAC and mean rate of change in septal and lateral regions with stimulation activated or turned off. See text for details.