The late-systolic murmur of mitral regurgitation (MR) in degenerative mitral valve disease is widely believed to represent regurgitation of a degree that is not associated with hemodynamic significance. However, the extent of left ventricular (LV) remodeling associated with the late-systolic murmur has not been systematically assessed. Accordingly, we studied 82 patients sent for evaluation of at least moderate isolated MR by echocardiography/Doppler examination. All patients had a physical examination and cardiac magnetic resonance imaging to measure LV volumes by summation of serial short-axis slices. Forty-five patients had a pan-systolic murmur and 37 had a late-systolic murmur on auscultation that was verified by timing of onset of regurgitant turbulence by cine magnetic resonance imaging. Systolic blood pressures (124 ± 3 versus 124 ± 3 mm Hg) and LV ejection fraction (61 ± 1% versus 61 ± 1%) did not differ significantly between pan-systolic and late-systolic murmur groups. Although LV end-diastolic volume index was greater in the pan-systolic versus late-systolic murmur (108 ± 4 versus 95 ± 4 mL/m, P = 0.007), both groups were significantly greater than normals (68 ± 2 mL/m, P < 0.0001). However, LV end-systolic volume index (42 ± 2 versus 38 ± 2 mL/m) and LV end-systolic dimension (38 ± 1 versus 37 ± 1 mm), critical markers of adverse LV remodeling in isolated MR, did not differ significantly between pan-systolic and late-systolic murmur groups. In conclusion, the late systolic isolated MR murmur may be associated with significant adverse LV remodeling, and should not be considered evidence of hemodynamically unimportant MR. © Copyright 2009 Southern Society for Clinical Investigation.