SUMMARY Since final mitral valve (MV) closure and aortic ejection velocity are mediated by the same forces in early left ventricular (LV) contraction, the rate of final MV closure (BC slope) should reflect LV performance. We first verified whether peak final closing velocity (ds/dt) of the anterior MV leaflet (AMVL) is related to peak aortic ejection velocity (V) and LV dp/dt in 18 open-chest dogs. We then checked the validity of the relations in man. Our approach was to measure peak ds/dt, peak aortic acceleration (dV/dt) and peak LV dp/dt using electronic differentiation of analog signals of the AMVL echogram, V and LV pressure. In dogs, resting ds/dt averaged 26.9 ± 9.0 (SD) cm/sec and changed significantly (P < 0.001) after isoproterenol, propranolol, coronary ligation and aortic cross-clamping. We found good (P < 0.001) correlations between ds/dt and V (r = 0.82), dV/dt (r = 0.67) and dp/dt (r = 0.73). In man, resting ds/dt averaged 25.5 ± 1.6 cm/sec in six normals. In 40 patients with coronary artery disease, resting ds/dt was lower (15.7 ± 4.4 cm/sec; P < 0.001) in the 19 with resting LV end-diastolic pressure (LVEDP) > 12 mm Hg. Resting ds/dt correlated closely with V (r = 0.82, N = 10), dp/dt (r = 0.93, N = 6), resting LVEDP (r = -0.67, N = 40), angiographic ejection fractions (r = 0.62, N = 40) as well as manually obtained BC slopes (r = 0.93, N = 40). Thus, final MV closing velocity provides a useful and simple means for the objective noninvasive assessment of LV performance.