The accuracy and reliability of two-dimensional monoplane and multiplane transesophageal echocardiography (TEE) in the quantitation of aortic valve area were compared in 54 patients with aortic stenosis. Fifty patients had aortic valve area calculated by the continuity equation and transthoracic Doppler echocardiography (TTE); 25 underwent cardiac catheterization. Two-dimensional echocardiograms adequate for quantitation of aortic valve area were obtained in 21 (39%) patients with monoplane TEE and in 51 (94%) with multiplane TEE. The mean aortic valve area determined by both TEE methods did not differ significantly from that derived from TTE and catheterization. The mean difference of aortic valve area measurements between monoplane TEE and TTE was -0.045 +/- 0.11 cm2; that between multiplane TEE and TTE was 0.001 +/- 0.11 cm2. Multiplane TEE provided a better correlation of aortic valve area measurements with either TTE (y = 0.97 x + 0.03; r = 0.96; SEE = 0.11 cm2) or catheterization (y = 0.84 x + 0.11; r = 0.90; SEE = 0.12 cm2) than the monoplane TEE (y = 0.88 x + 0.13; r = 0.83; SEE = 0.15 cm2 and y = 0.41 x + 0.42; r = 0.81; SEE = 0.15 cm2). Severe aortic stenosis with valve orifice area of < or = 0.75 cm2 during TTE examination was found by multiplane TEE with a sensitivity of 96% and a specificity of 96%. Thus aortic valve area can be directly and reliably measured by two-dimensional multiplane TEE in majority of patients with aortic stenosis.