Objective: We aimed 1) to investigate differences in left ventricular (LV) dyssynchrony according to types of LV hypertrophy in hypertophic cardiomyopathy (HCM) and 2) to relate it to LV mass index (LVMI). Methods: Ninety HCM patients (mean age, 55짹12years) were consecutively enrolled and assigned to one of the following 3 types – asymmetric septal hypertrophy (ASH, n=22), pure apical hypertrophy (ApHCM, n=57), and mixed ASH and ApHCM (mixed, n=11). LV dyssynchrony index (LVdys) was defined as standard deviation of time to peak radial strains from 6 myocardial segments at the papillary muscle level using 2D speckle tracking technique. LV mass was measured using area-length formula and indexed for body surface area. Results:. LVdys was markedly lower in the ApHCM than the other 2 groups (47.8짹36.6 vs, 136.1짹53.2 and 163.9짹79.7, both P<0.001. Figure A). With a cutoff value of 130msec as the upper limit of normal in LVdys, 63.6% in ASH, and 63.6% of mixed type had a LV dyssynchrony (P<0.001). As illustrated in Figure B, LVdys displayed a positive correlation with LV mass index (R=0.25). Conclusion: Although global LV systolic function as assessed with LV ejection fraction is preserved, LV dyssynchrony in HCM is not uncommon with an exception in ApHCM. Given the close relation between LV dyssynchrony and prognosis, relatively good prognosis in ApHCM could be explained at least partly by the lower prevalence of LV dyssynchrony.