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Background: In patients (pts) with significant left heart valve regurgitation the left ventricle (LV) reacts to volume overload by dilation and eccentric remodeling. In these pts, before the LV ejection fraction (LVEF) declines, more subtle LV systolic function abnormalities may be detected.Purpose. To perform a comparative assessment of parameters of LV function by TDI in asymptomatic pts with significant organic non-ischemic mitral regurgitation (MR) and in pts with chronic aortic regurgitation (AR), both with preserved LVEF (>55%) and similar degree of ventricular dilation.Methods. We prospectively enrolled 18 pts (44±17 years, 13 men) with moderate and severe pure AR and 10 pts with isolated moderate and severe organic non-ischemic MR (50±16 years, 8 men). A comprehensive echocardiogram was performed in all, including TDI-derived parameters of LV systolic and diastolic function. Averaged TDI-derived longitudinal LV strain and strain-rate (Sr) were assessed from apical 4-chamber view at septal site. The velocity of circumferential fiber shortening corrected to R-R interval (VCFSc) and the LV end-systolic wall stress were measured in all pts. LV end-systolic elastance (Ees) was calculated by a modified single-beat method using systolic and diastolic BP, stroke volume, EF, timing intervals and an estimated normalized ventricular elastance at arterial end-diastole (ENd): Ees=[Pd-(ENd(est) x Ps x 0.9)]/( ENd(est) x SV).Results. Age, gender and body mass index were not significantly different between groups (p >0.1 for all). Also, pts in both groups had similar LV diameters and volumes, indexed LV mass, LV sphericity index, LV shortening fraction, LV end-systolic wall stress and Ees (p>0.1 for all). LVEF was not significantly different between groups (61±3 in AR pts vs 63±3 in MR pts, p = 0.09). The relative LV wall thickness tended to be higher in AR patients (0.40±0.04 vs 0.36±0.05, p = 0.048). Pts with AR had lower S wave velocity at septal site than pts with MR (7.2±0.9 vs 9.4±1.9, p = 0.007). In pts with AR, both LV strain and SSr were significantly lower than in pts with MR (-17.9±3.8 vs -21.4±3.5%, p=0.023 and -1.0±0.2 vs -1.4±0.3 s-1, p=0.001, respectively). Also, VCFSc was lower in AR pts (0.11±0.02 vs 0.13±0.3 s-1, p=0.008). End-systolic wall stress significantly correlated with Sr values (r = 0.45, p = 0.02).Conclusions: Patients with AR have greater impairment of LV longitudinal and circumferential function than pts with MR, despite similar LV mass and volumes and preserved LVEF.