Analysis of a tapering, pulsatile flow field predicts that substantial subvalvular pressure gradients exist in patients with valvular aortic stenosis (AS) without invoking a second anatomic site of obstruction. Using a catheter with two laterally mounted micromanometers, we examined the left ventricle in 11 patients with AS, mean age 64 +/- 11 years (+/- SD); the mean valve area was 1.0 +/- 0.3 cm2. Simultaneous measurements were made in (1) the left ventricular (LV) chamber and the LV outflow tract (LVOT) and (2) the LVOT and ascending aorta (AO). No patient had anatomic evidence of a subvalvular obstruction, but large subvalvular gradients were present in all. The average peak LV-LVOT and LV-AO gradients were 41 +/- 17 mm Hg and 58 +/- 23 mm Hg, respectively. Flow velocity was electromagnetically derived in two patients. The LV-LVOT gradient was associated with an increased flow velocity in the LVOT. This study suggests that large subvalvular gradients are present in AS and help overcome blood's inertia to convective and local accelerations in the tapering subvalvular flow field.