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Figure 1 Representative steady-state pressure-volume diagrams from 1 patient with an ejection fraction (EF) 40% (A) and EF <40% (B). Groups during atrial overdrive pacing and during dual-chamber pacing and dual chamber biventricular (BiV) pacing. (C) Comparison of basal atrial overdrive (AAI) data from A and B. Rectangle in part A illustrates calculation of global cycle efficiency. Cycle efficiency is equal to the percentage of area occupied by the actual pressure volume loop within a rectangle determined by left ventricular (LV) pulse pressure and LV pulse volume. LVF = left ventricular free wall; RAA = right atrial; RVA = right ventricular apex; RVF = right ventricular outflow tract free wall; RVS = right ventricular outflow tract septum.