The ratio of early (Ep) to late (Ap) color M-mode Doppler flow propagation through the left ventricle helps in the differentiation between normal and pseudonormal (PSN) filling pattern in patients with preserved systolic function. We studied the value of this index in the assessment of diastolic dysfunction for patients with reduced left ventricular systolic function. We studied 80 patients with nonischemic dilated cardiomyopathy and 50 control subjects. According to echocardiography 53 patients had abnormal relaxation and 27 had PSN pattern. Patients had reduced Ep (P < .001) and Ep/Ap ratio (P < .001) and increased Ap (P = .001) compared to controls. Binary logistic regression analysis showed that Ep followed by Ep/Ap ratio (both P < .001) were the best determinants for the discrimination of PSN from normal filling pattern. Ep/Ap ratio, this novel echo-index, increases the diagnostic accuracy of color M-mode Doppler in discriminating normal from PSN filling pattern in patients with left ventricular systolic dysfunction.