Both mitral regurgitation and elevated left ventricular (LV) filling pressures may normalize or enhance rapid filling in patients with idiopathic dilated cardiomyopathy. To assess the individual effects of the LV filling pressure and mitral regurgitation, 33 normal subjects, 14 patients with cardiomyopathy and normal LV filling pressures (measured as mean pulmonary capillary pressure) and 26 patients with elevated LV filling pressures (>15 mm Hg) were studied with transmitral spectral tracings derived from pulsed Doppler echocardiography. Both cardiomyopathy groups demonstrated similarly dilated left ventricles with reduced systolic dysfunction. Patients with cardiomyopathy and normal LV filling pressures had prolonged isovolumic relaxation periods and a reduced ratio of the rapid filling to atrial filling integrals. Patients with cardiomyopathy and elevated LV pressures demonstrated an increased peak rapid fitting velocity (97 ± 21 cm/s) and rapid filling fraction (74.8 ± 16.2%) compared with normal subjects (80 ± 16 cm/s, p < 0.01; 62.4 ± 12.5%, p < 0.05) and patients with cardiomyopathy and normal LV filling pressures (81 ± 27 cm/s, p < 0.05; 59.3 ± 8.8%, p < 0.05). Conversely, the atrial filling fraction was decreased in the cardiomyopathy group with elevated LV filling pressures compared with normal subjects and patients with cardiomyopathy and normal LV filling pressures. Mitral regurgitation increased the peak rapid filling velocity in both cardiomyopathy groups without altering the distribution of diastolic filling. In conclusion, elevated LV filling pressures appear to affect the distribution of diastolic filling, whereas mitral regurgitation affects the peak rate of rapid filling.