Few observation have been made on the pericardial pressure and little is known about the composition of he pericardial fluid. So we studied the basic qualitative and quantitative analysis of the pericardial fluid in the patients with cardiac disease either congenital heart diasese(group A) or acquired heart disease(group B). The pressure of the pericardial cavity was measured by the method of open tipped water filled small polyethylene catheter connecting to the standardized monitor, which was introduced into pericardium of the patients who were performed pericardial incision for the heart or pericardial surgery. All of the data was compared to the simultaneously checked hematologic value of the same patient. The mean pressure of the pericardial cavity was 2.4mmHg and the amount of the pericardial fluid was 13cc/m2 of body surface for the group A and 17.7cc for the group B. And the cell count was 138$pm$l16/1 in group A and 230$pm$135/1 in group B and the pH was 7.83$pm$0.40 in group A. 7.80$pm$0.52 in group B. Pericardial fluid revealed satisfactically significant alkaline pH than plasma. The fundamental electrolyte, Wa+, K+, Cl and glucose were identical to the hematologic values of the same patient, but the protein concentration was 2.Bg/dL for group A and 3.Ig/dL for group B heart disease and those were remarkable low concentration compared to the hematologic value of the same patient. LDH and amylase were identical to the value of the serum of the same patient, but the concentration of LDH of group B was slightly higher than that of the group A.