BACKGROUND Lactate dehydrogenase (LDH) is an enzyme present in body tissue such as the heart, liver, skeletal muscle, brain, blood cells, and lungs. It is known that LDH level of normal pericardial fluid is 2.4 times that of serum. In contrast to pleural effusion or ascites, there are few data regarding the chemical and cell-count parameter of pericardial effusions to aid diagnosis. We aimed to evaluate the diagnostic value of LDH level in pericardial fluid in various etiology. METHODS A total of 44 patients who underwent pericardiocentesis during a 6-year period (2003 to 2009) were reviewed for biochemical and hemtologic test results for pericardial fluid and for blood. Of these, 9 patients were excluded due to iatrogenic hemopericardium or no available fluid record. We divided two groups: group A that didn���t invade pericardium or myocardium directly such as uremia or hypothyroidism: group B that invade pericardium or myocardium directly or relate to infection or inflammation of pericardial fluid such as malignancy, tuberculosis, infective pericarditis. RESULTS The most common cause of pericardial effusion requiring pericardiocentesis were neoplastic(40.9%) followed by iatrogenic(15.9%), idiopathic(4%), infection(9.1%), tuberculosis(9.1%), uremia(6.8%), connective tissue disease(4.5%) , hypothyroidism(4.5%). Level of adenosine deaminase (ADA) in pericardial fluids was significantly higher in tuberculous pericarditis compared with those of other causes (p<0.0001). No cell-count criteria proved valid for differentiating a single cause from other causes. Pericardial LDH level of group A was lower than that of group B (P=0.048). Pericardial/Serum LDH ratio in group A is lower than that in group B. Conclusion LDH level of pericardial effusion in systemic disease such as uremia and hypothyroidism is lower than that in other causes of pericardial effusion by direct invasion or infection.