Background – Recent studies provide evidence that vasoactive active substances are present in the pericardial fluid (PF), which levels may change in cardiovascular diseases. Increasing evidence suggests that methylated L-arginine derivative, asymmetric dimethylarginine (ADMA) is a risk factor of most cardiovascular diseases. Furthermore, it has been shown that ADMA inhibits endothelium-dependent vasodilation by interfering with endothelial nitric oxide (eNOS) activity and/or eliciting oxidative stress, both of which interfere with the bioavailability of endothelium derived nitric oxide (NO). We hypothesized that ADMA levels in the PF reflects/contributes the pathological processes in the heart. Methods and patients – Patients were classified into two groups according to the type of surgery: coronary artery bypass graft (CABG, n = 28) and valve replacement (VR, n = 16). Blood and PF were collected during CABG and VR surgery. Levels of L-arginine and ADMA were determined in plasma and PF (with fluorescent detection after liquid chromatographic separation) of patients underwent CABG and VR surgery, compared them and an indicator of eNOS substrate availability, L-arginine/ADMA ratios were calculated. Values are expressed as means ± S.E.M. Comparisons between groups were performed using paired Student’s t-test. Results – We found that in CABG group, the L-arginine levels were similar in plasma and PF (75.7±4.6 micromol/L vs. 76.9±4.4 micromol/L). In VR group, the L-arginine levels were significantly (p<0.05) lower in plasma compared to the PF (57.7±5.9 micromol/L vs. 71.5±5.7 micromol/L). In CABG group, the ADMA levels were the same in plasma and PF (0.7±0.0 micromol/L vs. 0.7±0.1 micromol/L). In VR group, the ADMA levels were similar in plasma and PF (0.8±0.1 micromol/L vs. 0.9±0.1micromol/L). In CABG group, the L-arginine/ADMA ratios were significantly higher compared to the VR group in both plasma (125.4±10.7 vs. 74.9±8.3) and PF (110.4±7.2 vs. 79.5±5.8). Conclusion – Based on these findings we propose that the lower L-arginine/ADMA ratios suggest increased methylation of L-arginine and limited substrate availability for eNOS and thus impaired nitric oxide signaling and vascular function in patients with heart valve disease. Keywords: pericardial fluid, vasoactive active substances, coronary heart disease, L-arginine, asymmetric dimethyl arginine, nitric oxide.