Using pulsed Doppler echocardiography, blood filling patterns of the right atrium and left and right ventricles in constrictive pericarditis were studied to evaluate the physiological role of the pericardium in the hemodynamics of this disease. Thirteen cases were examined including five cases with atrial fibrillation. The control subjects consisted of 16 healthy persons and six cases of lone atrial fibrillation. 1. Peak velocity of the atrial filling wave during ventricular systole was reduced, and the filling time was shortened, suggesting reduced compliance and restricted motion of the atrial wall, because of the thickening and adhesions of the pericardium. Duration of the atrial filling wave during ventricular diastole was also shortened, reflecting disturbance of the early diastolic filling of the right ventricle. 2. In healthy subjects, duration of the rapid filling wave was longer in the right ventricle than in the left ventricle, probably due to the greater compliance of the right ventricular wall as compared to that of the left ventricular wall. In constrictive pericarditis, the rapid filling time of the right ventricle is shortened, so that the difference in this time between the right and left ventricles is minimized, which may be related to a thinner right ventricular wall. Duration of the rapid filling wave of the right ventricle correlated with right ventricular end-diastolic pressure, indicating that the duration of the right ventricular rapid filling wave is proportional to the severity of constrictive pericarditis. In conclusion, constriction of the pericardium definitely influences the hemodynamics of the right side of the heart more than it does the left side in constrictive pericarditis. This difference appears to result from the difference in thickness of the myocardial layers of both ventricles.