Real time two-dimensional echocardiographic studies of left ventricular outflow tract cross-sectional anatomy were obtained by the multicrystal echocardiographic method (Bom system) in 35 patients with various types of outflow obstruction as delineated by clinical, hemodynamic and angiographic studies. In each patient the noninvasive test allowed prediction of the site of obstruction. In valvular aortic stenosis, echocardiographic diagnostic findings included poststenotic dilatation of the ascending aorta, thickened aortic cusp tissue and increased superior-inferior cusp excursion (doming). The site of supravalvular aortic stenosis was readily observed although echocardiographic findings often underestimated the degree of obstruction recorded at cardiac catheterization. In patients with discrete subvalvular aortic stenosis, the major finding was a localized thickening of the septum and anterior mitral anulus producing a narrowing of the left ventricular outflow tract that was present in diastole and persisted throughout the cardiac cycle.