To evaluate the propagation velocity of isovolumic relaxation flow within the left ventricle (IRFPV) associated with impaired ventricular relaxation, 49 patients with diseases known to impair ventricular relaxation (disease group) and 38 age-matched control subjects (control group) were studied. IRFPV was measured as the slope of the first aliasing velocity line segment of the isovolumic relaxation flow wave front in the color M-mode Doppler echocardiogram. Compared with the control group, the disease group had thicker interventricular septum and left ventricular posterior wall, more left ventricular mass, and lower early diastolic mitral annular velocity (8 +/- 3 vs 11 +/- 4 cm/s, P < .001), early (E) wave propagation velocity (47 +/- 16 vs 70 +/- 41 cm/s, P = .002), and IRFPV (193 +/- 149 vs 395 +/- 220 cm/s, P < .001). No matter in subgroup or whole population analysis, either the early diastolic mitral annular velocity or the E wave propagation velocity was selected as one of the determinants of IRFPV. In conclusion, diseases impairing ventricular relaxation may retard IRFPV.