Objective To assess left ventricular torsional mechanics in patients with chronic severe aortic regurgitation(AR) by three dimensional strain imaging and to assess the effect of aortic valve replacement (AVR) on left ventricular (LV) twist function. Method we studied with two dimentional echocardioraphy 30 normal subject, 40 patients with chronic severe AR with LVEF≥55%(AR-A), 36 patients with LVEF＜55%(AR-B). Conventional LV volume, function, geometry indexes including LVEDD, LVESD, LVEDVI, LVESVI, LVMI , LVEF, LV sphericity index(LVSI), LV remodeling index(LVRI) were measured and calculated by 2D echocardioraphy. LV basal rotation, apical rotation and time to peak rotation, LV torsion and time to peak twist by Tomtec workstation 3D-STI were analyzed and compared among subgroups. Among all patients,31 have undergone aortic valve replacement, 2D and 3D echocardiography were performed 2 weeks after operation. Result (1)As compared to normal control, Torsion and RoA was significantly reduced in AR-A(p＜0.05), while RoB was preserved(p＞0.05).LV torsion,RoA and RoB were all significantly decreased in AR-B(p＜0.05). (2)As compared to normal control, time to peak twist and time to peak RoB were longer in AR-A(P＜0.05), Time to peak twist ,time to peak RoA and RoB were shortened in AR-B(P＜0.05). (3)Multiple linear regression analysis confirmed that Torsion was affected by LVEF and LVSI.RoA wasSindependentlySassociatedSwith LVSI. RoB was affected by both LVEF and LVRI. (4) 2 weeks after aortic valve replacement, left ventricular volume , dimensions and EF decreased significantly(all p＜0.01). Torsion and ROA were significantly increased(p＜0.05), but RoB did not differ from preoperation. Conclusion Three dimensional speckle tracking could quantitatively assess the left ventricular torsional dynamics in severe AR patients and contribute to a deeper understanding of subtle mechanic changes of left ventricular which couldn’t be detected by conventional echocardiography parameters. Parameters of torsional dynamics can sensitively reflect the improvement of left ventricular myocardial function after operation.