Abstract: Objective To explore the effects of proadrenomedullin N-terminal 20 peptide (PAMP) on nitric oxide (NO) production in rat cardiac fibroblasts (CFs) induced by angiotensin II (AngII) stimulation. Methods Neonatal SD rat CFs isolated by trypsin digestion were cultured and stimulated with PAMP, AngII or their combination, and NO production in the CFs in response to the treatments was measured by nitric acid reductase method. Results NO levels in the cell culture treated with 1×10-9, 1×10-8, 1×10-7, and 1×10-6 μmol/L AngII were 73.88±2.23, 64.34±3.02, 54.12±2.82, and 40.21±1.45 μmol/L, respectively, showing significant differences between the groups (P<0.01), whereas treatment of the cells with 1×10-9, 1×10-8, 1×10-7, and 1×10-6 μmol/L PAMP did not result in significant variation in NO production (74.40±3.42, 74.91±2.66, 75.77±3.31, and 74.23±2.43 μmol/L, respectively) in comparison with that of the blank control group (74.57±2.49 μmol/L, P>0.05). Combined treatments with 1×10-7 μmol/L AngII and PAMP at 1×10-9, 1×10-8, 1×10-7, and 1×10-6 μmol/L PAMP caused significant increment of NO production (66.15±2.95, 80.58±3.77, 88.67±1.46, and 96.22±2.96 μmol/L, respectively, P<0.01) in a PAMP dose-dependent manner, suggesting the abolishment of AngII-induced enhancement of NO production in the CFs by PAMP. Conclusion PAMP increases NO production in the CFs in the presence of AngII but it does not induce significant changes in NO production when used alone.