Effective orifice area (EOA) is the standard index for assessing aortic stenosis (AS) severity. However, EOA varies during ejection and a single measurement at 1 ejection time point may not fully describe the hemodynamic severity of a stenotic aortic valve. We investigated whether the dynamic change in EOA during ejection differs between patients with severe AS (EOA </= 1.0 cm(2)) (n = 15) and age-/sex-matched control patients (n = 15), and whether the ejection pattern varies with AS severity (n = 45). In patients with severe AS, maximum left ventricular outflow tract velocity (V(LVOT)) and transvalvular velocity (V(AS)) occurred later in the ejection period (EP) when compared with control patients (V(LVOT) 47 +/- 8 vs 29 +/- 8%, P =.0001; V(AS) 36 +/- 7 vs 27 +/- 8%, P =.003). Maximum V(LVOT) occurred later than maximum V(AS) in patients with severe AS (47 +/- 8 vs 36 +/- 7%, P =.0005), but simultaneously in control patients (29 +/- 8 vs 27 +/- 8%, P = NS). Patients with severe AS had a slower EOA opening rate than control patients (4 +/- 1 vs 41 +/- 38 cm(2)/s, P =.002) and reached 80% and 100% of maximum EOA later in the EP (43 +/- 26 vs 15 +/- 6%, P =.001; 70 +/- 20 vs 48 +/- 30%, P =.03). EOA tended to increase between 10% and 90% of the EP in patients with severe AS, but had a plateau in control patients (slope 0.38 +/- 0.26 vs 0.02 +/- 0.25% change in EOA per 1% change of EP, P =.0006). In patients with severe AS, EOA was >/=80% of maximum EOA for a shorter duration during ejection compared with control patients (49 +/- 25 vs 64 +/- 14%, P =.05). EOA opening rate, time to maximum V(LVOT), time to maximum V(AS), and time to 80% of maximum EOA correlated with mean pressure gradient (r = -0.80, 0.63, 0.42, and 0.54, respectively, n = 45). Indices of ejection dynamics and valve kinetics differ in patients with AS and may provide further insight into the hemodynamic or physiologic severity of a stenotic aortic valve.