The rate of left ventricular (LV) pressure fall (dP/dtmin) is reportedly altered by contractility and LV stress. To explore the possibility that the ratio of dP/dtmin to dicrotic notch pressure (DTES) measures contractility, 243 subjects including 23 normals (group I) were studied. In 35 patients of group II (16 with mitral stenosis, 7 with atrial septal defect, and 12 with cor pulmonale) DTES, as an index of contractility (Cy Ix) measuring force-velocity-length relationship, was insignificantly different from group I (DTES and Cy Ix in group I = 21.6 ± 0.6 s-1 and 1.34 ± 0.04 muscle lengths/s/cm and 18.8 ± 1.8 s-1 and 1.55 ± 0.24 muscle lengths/s/cm in group II, respectively). With significantly reduced Cylx (1.05 ± 0.04, p < 0.01), DTES was likewise reduced (19.0 ± 0.5, p < 0.01) in 163 patients with compensated LV disease (47 with alcoholic cardiomyopathy, 24 coronary artery disease, 48 valve disease, 10 hypertensives and 34 with other heart muscle diseases). Like the Cy Ix (0.70 ± 0.05, p < 0.001), DTES was even lower (13.3 ± 0.6, p < 0.001) in 15 patients with decompensated LV (group IV). Like Cy Ix, this ratio changed significantly with acute changes in inotropy (exercise and pacing), but not with preload (dextran infusion). Basal heart rate, preload and afterload did not influence DTES. Furthermore, DTES correlated significantly in all groups and subgroups with two indices of contractility, VCE(velocity of contractile element) at peak isometric stress, and Cy Ix (r = 0.68 and 0.70, respectively, each p < 0.001) measured in this study. These results indicate that DTES provides a simple, reliable, and useful measure of the contractile state of LV myocardium in man, independent of preload and afterload.