Since mitral valve (MV) complex (MVC) longitudinally bridges left ventricular (LV) base-end and its middle, insufficient MVC longitudinal tissue length (TL) elongation relative to whole LV myocardial longitudinal TL elongation could limit LV-base-longitudinal-TL elongation, leading to predominant LV-base-transverse-TL elongation, constituting LV spherical remodeling. In 30 patients with dilated cardiomyopathy (DCM), 30 with aortic regurgitation (AR), and 30 controls, LV sphericity, LV-apex- or base- transverse- and longitudinal-TL, MVC-longitudinal-TL and whole-LV-longitudinal-TL were measured by 3D echocardiography. Ratio of each measure vs. mean normal value (i.e., LV-apex-transverse-TL ratio) was considered to express the directional and regional tissue elongation. [LV-base-longitudinal-TL ratio/global-LV-TL ratio] and [MVC-longitudinal-TL ratio/whole-LV-longitudinal-TL ratio] were obtained as the degree of LV-base-longitudinal-TL or MVC-longitudinal-TL elongation relative to the whole LV elongation. LV-apex-transverse-, LV-apex-longitudinal- and LV-base-transverse-TL ratios were significantly increased (1.27 to 1.42, p<0.01) in both DCM and AR, while the LV-base-longitudinal-TL ratio was not increased in DCM (1.04±0.19, n.s.) and only modestly increased in AR (1.12±0.21, p<0.01). Whole-LV-longitudinal-TL ratio was significantly increased in both DCM and AR (1.22±0.18 and 1.20±0.16, p<0.01), while MVC-longitudinal-TL ratio was not or only modestly increased in both groups (1.07±0.15, n.s. and 1.12±0.17, p=0.02, respectively). Multivariable analysis revealed that LV sphericity was independently related to a reduced [LV-base-longitudinal-TL ratio/global-LV-TL ratio] (standard β=-0.42, p<0.01), which was further related to a reduced [MVC-longitudinal-TL ratio/whole-LV-longitudinal-TL ratio] (standard β=0.72, p<0.01). These are consistent with the hypothesis that relatively less MVC-longitudinal-TL elongation in the process of primary LV myocardial tissue elongation may limit LV-base-longitudinal-TL elongation, contributing to LV spherical remodeling.