Different cross-sectional echocardiographic patterns of systolic anterior motion of the mitral valve (SAM) have been observed in patients with hypertrophic cardiomyopathy. chordae tendineae and/or the free edge of the mitral valve were seen to be involved in some: SAM(c). The body of the mitral valve encroached upon the left ventricular outflow tract in this movement in a second group: SAM(v). Other patients did not show SAM. A study of 27 patients was performed to investigate the relationship of these patterns of SAM to the subaortic gradient as well as the prevalence and degree of mitral regurgitation. The absence of SAM correlated with no obstruction and 29% prevalence of mitral regurgitation. In SAM(c), the mean gradient was 10 +/- 10 mmHg. (0-35 mmHg), and mitral regurgitation involved 36% of the patients. In SAM(v) the mean gradient found was 81 +/- 37 mmHg (20-150), and 67% had mitral regurgitation. In situations where mitral regurgitation was most prevalent its degree was greatest. CONCLUSIONS (1) chordal or leaflet participation in SAM is relevant to the presence and degree of obstruction; (2) leaflet involvement usually implies severe obstruction; (3) distortion of the mitral valve apparatus may contribute to the genesis of mitral regurgitation.