The pericardial fluid BNP and plasma BNP concentrations were measured in 18 patients underwent surgical repair of ventricular septal defect (VSD). The levels of BNP in the pericardial fluid (324.8 ± 137.3 pg/ml) were higher than that in the plasma (20.75 ± 6.05 pg/ml) (P=0.034). Pericardial fluid BNP was correlated with the plasma BNP (r=0.85, p<0.01). A good correlation was also found between the pericardial fluid BNP levels and left atrial diameter, left ventricular end-diastolic and end-systolic diameter, left ventricular ejection fraction, right ventricular diameter and mean pulmonary artery pressure (p<0.05). We conclude that the levels of BNP in pericardial fluid were higher than that in the plasma. Similar to plasma BNP, pericardial fluid BNP is also related to the ventricular diameter and function.