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Hemodynamically significant mitral regurgitation (MR) may alter left ventricular (LV) myocardial energy requirements. The effects of MR and subsequent corrective mitral valve (MV) surgery on myocardial energetics are not well understood. A better understanding of myocardial energetics and the LV responses to changes in preload and afterload may assist with the understanding of mitral regurgitation and its effect on the LV. We sought to determine the effects of MV surgery on forward stroke work, myocardial oxidative metabolism, and myocardial efficiency.Prospectively enrolled patients with chronic, severe, nonischemic mitral regurgitation underwent echocardiography, radionuclide angiography, and C-11 acetate positron emission tomography to measure LV volumes, ejection fraction, and oxidative metabolism before and 1 year after MV surgery. Forward and total stroke work corrected for oxidative metabolism was used to estimate efficiency using the work metabolic index. Fourteen patients (age, 59± 8 years) with myxomatous MV were enrolled. One year after MV surgery, there was a reduction in LV end-diastolic and end-systolic volumes (231±86 to 131±21 mL; P<0.01 and 98±53 to 55±17 mL; P<0.01). Forward stroke volume increased (58.1±15.0 to 75.5±23 mL; P<0.01), LV ejection fraction was preserved without a significant change in oxidative metabolism. Forward work metabolic index improved (4.99±1.32×106 to 6.59±2.45×106 mm Hg×mL/m2; P=0.02). This was not at the expense of total work metabolic index, which was preserved.MV surgery has a beneficial effect on forward stroke volume and forward work metabolic index without adverse effects on oxidative metabolism or total work metabolic index.