Background: Assessment of left ventricular (LV) contractile function is crucial in patients with chronic severe mitral regurgitation (MR). Chronic LV remodeling in the presence of severe MR may have different impact on long-axis and short-axis function. We investigated LV long-axis and short-axis function in chronic severe MR. Methods and Results: We prospectively enrolled 36 patients (18men, age: 53짹12 years) who had severe MR with LV ejection fraction (EF) greater than 50%. Mean LV end-diastolic and end-systolic volume indexes were 125짹25, 48짹12ml/m2, respectively. LV EF was 62짹6%, and regurgitant fraction 66짹10%. Peak systolic radial (SRR), circumferential (SRC), and longitudinal strain rate (SRL) were measured using speckle tracking imaging. LV peak dP/dt was measured using micromanometer-tipped catheter. Peak dP/dt ranged from 1024 to 2049 mmHg/s (mean: 1342짹246 mmHg/s). SRR and SRC correlated well with peak dP/dt (r=0.74, p<0.001; r=-0.58, p<0.001, respectively) whereas SRL did not correlate. SRR > 1.9 S-1 showed a sensitivity of 86% and a specificity of 75% for preserved contractile function (dP/dt���1300 mmHg/s). To verify the effect of LV remodeling on this difference between short-axis and long-axis function, we measured geometric parameter, sphericity index. SRR correlated with LV end-diastolic and end-systolic sphericity indexes (r=-0.55, p=0.001; r=-0.65, p<0.001, respectively), but SRL did not. We compared echocardiographic parameters between age-, sex- matched normal control (n=36) and MR patients with preserved (dP/dt���1300 mmHg) (Gr 1, n=17) or with depressed (Gr 2, n=19) contractile function. Gr 1 MR patients showed similar SRR and SRC with normal control, but lower SRL than control. In contrast, Gr 2 MR patients showed lower SRR, SRC, and SRL than normal control, suggesting that SRL decreased earlier than SRR and SRC in the progression of LV remodeling. Conclusions: SRR and SRC, not SRL, correlated well with peak dP/dt. These results imply the importance of LV short-axis function with the LV remodeling in response to chronic MR. LV short-axis function may be better than long-axis function as an indicator for global LV contractile function in chronic severe MR.