Abstract: AIM To investigate the effects of simvastatin (Sim) on the proliferation and collagen synthesis of rat cardiac fibroblasts (CF) induced by arginine vasopressin (AVP). METHODS CFs of neonatal SpragueDawley (SD) rats were isolated by trypsin digestion method and the growtHarrested CFs were stimulated with 0.1 μmol/L AVP in the presence of varying concentrations of Sim (0.01 μmol/L-10 μmol/L) and MVA (1 μmol/L-1 mmol/L). Collagen synthesis was measured by3Hproline incorporation and the cell number was evaluated by MTT. RESULTS The results showed that: ①Sim decreased3Hproline incorporation in CFs in a concentrationdependent manner.3Hproline incorporation values of 1 μmol/L Sim 3Hproline group and 10 μmol/L Sim group (3.67±0.39 mBq/cell and 2.35±0.36 mBq/cell, respectively) were significantly lower than that of the control (5.01±0.58 mBq/cell，P<0.01). ②The absorbance A490 values by MTT assay decreased with the elevation of Sim concentration. The A490 values of 1 μmol/L Sim group and 10 μmol/L Sim group (0.221±0.038, 0.163±0.021, respectively) were significantly lower than that of the control (0.395±0.039，P<0.01). ③3Hproline incorporation in CFs and the A490 value of 10 μmol/L Sim+1 mmol/L MVA group (5.38±0.72 mBq/cell and 0.419±0.051, respectively) were significantly higher compared with those of 10 μmol/L Sim group (P<0.01). CONCLUSION The results indicate that Sim decreases CF number and collagen synthesis induce by AVP and that MVA pathway may play an important role in the CF proliferation and collagen synthesis.