Left ventricular (LV) ejection fraction (LVEF) is currently considered for the decision making of patients with mitral regurgitation (MR). However, LVEF represents change in LV volume between end-diastole and end-systole but does not characterize the intrinsic function of the myocardium. In contrast, speckle-tracking global longitudinal strain (GLS) characterizes myocardial deformation. The present study evaluated whether LV GLS may detect further impairment in LV systolic function in dilated cardiomyopathy patients with and without severe secondary MR matched based on LVEF.