Doppler ultrasound has been used to determine the pressure gradient P1-P2 across the valve in patients with aortic stenosis (AS), but since the gradient varies over time and may be deceptively low in patients with impaired cardiac output, the key parameter to obtain is the orifice area (A). By calculating stroke volume (SV) from the modal flow velocity [Vmode(t)] over the systolic ejection period (sep) or diastolic filling period (dfp), wherever laminar flow exists in the heart across an area of known diameter D, (pulmonary artery or atrioventricular valves), and by substituting P1-P2 = 4Vmax2, (Vmax = peak velocity in the aortic jet), the Gorlin formula becomes: (Formula: see text) where theta = flow intercept angle at D. This approach was applied in nine adult patients with AS (age 64 +/- 8 years) in whom recent catheterization data was available for comparison. Close correlation was found between the calculated areas: A(Doppler) = 0.82 A(Cath) + 0.17 (r = 0.94, p less than 0.001). Two patients with Doppler gradients of less than 40 mmHg were shown by this Doppler method nevertheless to have severely narrowed orifice areas of less than or equal to 0.78 cm2. Although there is a tendency to overestimate slightly the valve area, Doppler ultrasound assessment using this technique adds valuable noninvasive information concerning the degree of aortic valve disease.