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Background—Left ventricular or biventricular pacing/stimulation can acutely improve systolic function in patients with dilated cardiomyopathy (DCM) and intraventricular conduction delay by resynchronizing contraction. Most heart failure therapies directly enhancing systolic function do so while concomitantly increasing myocardial oxygen consumption (MVO₂). We hypothesized that pacing/stimulation, in contrast, incurs systolic benefits without raising energy demand.

Methods and Results—Ten DCM patients with left bundle-branch block (ejection fraction 20±3%, QRS duration179±3 ms, mean±SEM) underwent cardiac catheterization to measure ventricular and aortic pressure, coronary blood flow, arterial–coronary sinus oxygen difference (ΔAVO₂), and MV̇O₂. Data were measured under sinus rhythm or with left ventricular or biventricular pacing/stimulation at the same heart rate. These results were then …