The exact determination of the severity of valvular heart disease represents the basis for the indication for surgery. Apart from the clinical findings, the estimation of the severity has, up to now, been based on the chest x-ray, the electrocardiogram, and the carotid pulse curve. By means of cardiac catheterization, the aortic valve gradient is determined and the aortic valve area is calculated using the Gorlin equation. Doppler echocardiography allows for a noninvasive gradient assessment. The peak and mean pressure gradients as well as the aortic valve area can be calculated. Echocardiography provides additional information about the severity of the left-ventricular hypertrophy, the heart size, as well as about secondary complications. Doppler echocardiography was performed in 95 patients to determine the peak pressure gradient. This Doppler-derived gradient correlated well with the catheterization-derived invasive gradient. The correlation coefficient was r = 0.81, for the mean gradient r = 0.77, and for the aortic valve area r = 0.87. Based on the classical determination of the severity of aortic stenosis by means of cardiac catheterization, a Doppler-derived mean pressure gradient > 54 mm Hg or a peak pressure gradient > 89 mm Hg and an aortic valve area > 0.7 cm2 are specific for severe aortic stenosis. A mean pressure gradient between 40 and 54 mm Hg or a peak pressure gradient of 67 and 89 mm Hg and an aortic valve area of 0.7 and 1.3 cm2 indicate moderately aortic stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)