Systolic anterior motion (SAM) of the mitral valve in the absence of asymmetric septal hypertrophy or concentric left ventricular hypertrophy has been reported in several conditions. In this report we describe the clinical and echocardiographic findings in 15 patients who demonstrated SAM without associated organic heart disease (group 1, 10 patients) or in association with mitral valve prolapse (group 2, five patients). Cross-sectional echocardiography revealed the etiology of SAM in both groups to be early systolic anterior angular motion ("buckling") of mitral chordal structures, rather than movement of the body of the anterior mitral leaflet into the left ventricular outflow tract. In contrast to normal subjects and group 1, group 2 patients had auscultatory evidence of mitral prolapse, a slightly greater mean left ventricular ejection fraction (p < 0.05) (normals, 69 +/- 5.2%, group 1, 72 +/- 3.8%, group 2, 75+/- 5.6%), and a greater mean diastolic mitral valve (D-E) excursion (p < 0.05) (normals, 1.8 +/- 0.2 cm, group 1, 2.2 +/- 0.3 cm, and group 2, 2.6 +/- 0.4 cm). This spectrum of mitral excursion and left ventricular ejection fraction supports the concept that the mitral valve prolapse syndrome may have as its basis a mitral valve abnormality and/or a hyperdynamic state that predispose to both chordal buckling and mitral leaflet prolapse.