Background: Mechanical asynchrony has been shown to be a predictor of ventricular function and future remodeling in patients with heart failure. Objectives: We sought to investigate prevalence and determinants of intraventricular asynchrony in patients with compensated severe aortic regurgitation (AR) by comparing that of dilated cardiomyopathy (DCM). Methods: Patients with severe isolated AR and LV ejection fraction >50% and LV end-diastolic dimension >55 mm were enrolled. Nonischemic DCM patients as a positive control and healthy subjects were also studied. Patients with QRS duration > 120 ms were excluded in all groups. After comprehensive echo-Doppler measurements, standard deviation of time to peak longitudinal contractions (Ts-SD) and relaxations (Te-SD) in 12 LV segments were measured. Right ventricular (RV) function was measured by longitudinal Doppler strain in free wall. Results: Ts-SD and Te-SD of DCM (n=36) and AR (n=35) were significantly higher than that of control (n=20) (Ts-SD: 46.6 짹 13.4 ms for DCM vs. 51.2 짹 11.4 ms for AR vs. 13.1 짹 5.6 ms for control, p<0.0001; Te-SD: 33.4 짹 12.2 ms vs. 38.5 짹 14.9 ms vs. 12.5 짹 2.9 ms, respectively, p<0.0001). Despite higher LV ejection fraction (64.0 짹 6.4% vs. 22.1 짹 8.5 %, p<0.0001) and comparable LV-end diastolic dimension (65.6 짹 7.9 mm vs. 68.8 짹 5.9 mm. p=0.146) in AR, prevalence of intraventrcular asynchrony, defined as Ts-SD >37 ms (88.2% in AR vs. 68.4% in DCM, p=0.236), absolute Ts-SD (p=0.282) and Te-SD (p=0.186) were comparable between two groups. In patients with AR, Te-SD was significantly correlated with LV ejection fraction (r=-0.383, p=0.023), LV end-systolic dimension (r=0.457, p=0.006) and RV strain (r=0.450, p=0.007). Conclusions: Patients with compensated AR also shows significant intraventricular asynchrony with close relationship to biventricular function.