The filling modes into the right atrium and both ventricles were observed using pulsed Doppler echocardiography in six cases of restrictive myocardial diseases, and these were compared with those of 13 cases of constrictive pericarditis, six cases of lone atrial fibrillation and 16 healthy subjects. Special attention was paid to the mechanical properties of the cardiac walls which might be reflected in the filling modes. 1. In the restrictive cases, right atrial filling from the superior caval vein during ventricular systole was reduced in velocity and duration, but the atrial filling during ventricular diastole was not appreciably changed. This flow pattern was similar to that of lone atrial fibrillation, indicating reduced distensibility or impaired contraction and ejection fraction of the right atrium. In constrictive pericarditis, the right atrial filling time was shortened both in ventricular systole and diastole, reflecting stiffening of the pericardium. 2. In the restrictive cases, the first half of the left ventricular rapid filling wave was steep and the skirt of the descending limb was prolonged, while there was no such tendency in the right ventricle. In constrictive pericarditis, the rapid filling time was shortened in the right ventricle, and was not significantly changed in the left ventricle. 3. The differences in the atrial and ventricular filling patterns between restrictive myocardial disease and constrictive pericarditis may serve to distinguish these two disease entities.