Clinical and laboratory studies on three cases of constrictive pericarditis were carried out in the period of time between pre- and postpericardiectomy. Two of them were restored and one died 27 days after the operation and was autopsied. In all cases the past history supported the probable diagnosis of pericarditis of tuberculous origin. The major signs in these cases were ascites, peripheral edema, hepatosplenomegaly and engorgement of the jugulal veins. Some manifestations like hypoproteinemia, increased sedimentation rate, elevated venous and spinal fluid pressure, low arterial blood pressure, small pulse pressure, and prolonged circulation time were in accord with those observed by many other authors. The X-ray findings; the cardiac pulsation were definitely decreased or almost completely absent and a few plaques of calcification were found by tomography. The electrocardiogram; flat and/or comparatively sharply or deeply inverted T weves in all cases and auricular fibrillation in one case were seen but low voltage of QRS complexes was not seen in any case. The angiocardiogram; dilatation of the superior vena cava and the small aortic arch were shown. The regurgitation of the contrast material into the inferior vena cava was also demonstrated and this is considered as a prominent sign in the diagnosis. The liver biopsy; marked congestion was found without any change suspected of being hepatic cirrhosis. The hemodynamic studies in the usual way by means of right heart catheterization revealed a rise of the blood pressure at any site in the range between the systemic vein and the “pulmonary capillary”, and the so-called “early diastolic dip” was recorded in the right ventricle. The cardiac output was low and its level was not affected by the reduction of the venous return induced by the tourniquets applied on both thighs. Dye-dilution curves obtained at the brachial arteries indicated a curve similar to normal but not a alow one as is usually seen in congestive heart failure. The decortication of the heart improved the morbid conditions of the hemodynamics but such symptoms as peripheral edema, ascites, and hepatosplenomegaly remained unchanged, or were slightly improved. From above studies we would like to draw the conclusion that the surgical treatment for constrictive pericarditis should be performed as soon as possible after the diagnosis has been made.