Baseline echocardiographic data in 680 adults (mean age 78 years) undergoing balloon aortic valvuloplasty at 24 medical centers were analyzed to describe the degree of outflow obstruction in patients with symptomatic aortic stenosis. Maximal aortic jet velocity ranged from 2.3 to 6.6 m/s (mean 4.4 +/- 0.8) and continuity equation valve area ranged from 0.1 to 1.4 cm2 (mean 0.6 +/- 0.2). Of note, 36% had a jet velocity less than or equal to 4.0 m/s but only 3% had a valve area greater than 1.0 cm2 due to a high prevalence of impaired systolic function (54%). Outflow tract diameter was poorly correlated with body surface area (p = 0.26), although the group mean diameter was smaller in women than in men (1.9 +/- 0.2 vs 2.1 +/- 0.3 cm, p = 0.0001). Mean pressure gradient was related closely to maximal gradient (r = 0.92) and to maximal jet velocity (mean delta P = 2.4 V2 + 0.75 mm Hg). Simpler measures of aortic stenosis severity were correlated with Doppler and invasive valve area as follows: maximal jet velocity (r = -0.36 and -0.32), mean gradient (r = -0.33 and -0.29), outflow tract to jet velocity ratio (r = 0.67 and 0.40), and the fractional shortening velocity ratio (r = 0.29 and 0.22). This study demonstrates marked variability in stenosis severity in symptomatic adults referred for balloon aortic valvuloplasty. The absence of a predictable relation between outflow tract diameter and body size emphasizes the importance of this measurement in each patient if definition of valve area is needed.(ABSTRACT TRUNCATED AT 250 WORDS)