Objective To investigate the regulatory effect and possible mechanism of lactic acid on the fibrotic phenotype of cardiac fibroblasts.Methods Mouse cardiac fibroblasts(mCFs)were divided into control group(conventional culture),experimental-L group(4 mmol·L-1 L-lactic acid),experimental-M group(8 mmol·L-1 L-lactic acid),experimental-H group(12 mmol·L-1 L-lactic acid),transforming growth factor-β1(TGF-β1)group(10 ng·mL-1 TGF-β1),combined group(10 ng·mL-1 TGF-β1+12 mmol·L-1 L-lactic acid)and monocarboxylate transporter inhibitor(CHC)group(3 mmol·L-1 CHC).Western blot was used to detect the expression of fibrosis-related proteins and pan-lactate modification(Pan Kla)and H3 histone K18 lactate modification;cell scratch assay was used to detect cell migration ability.Results The cell migration rates of the control group,TGF-β1 group,experimental-H group and combined group were(40.56±0.03)%,(61.61±0.04)%,(26.59±0.05)%and(38.33±0.06)%,respectively.Compared with the control group,TGF-β1 group and experimental-H group,TGF-β1 group and combined group,the differences were statistically significant(all P<0.01).The relative expression levels of collagen type Ⅰ alpha 1(COL1A1)protein in the control group,TGF-β1 group,experimental-H group and TGF-β1+experimental-H group were 0.76±0.09,1.10±0.07,0.40±0.04 and 0.68±0.10,respectively;the relative expression levels of COL3A1 protein were 0.87±0.05,1.15±0.07,0.32±0.07 and 0.73±0.06,respectively;the relative expression levels of α-smooth muscle actin(α-SMA)protein were 0.86±0.04,1.24±0.09,0.30±0.05 and 0.74±0.08,respectively.Compared with the control group,the above indexes of the TGF-β1 group and the experimental-H group were significantly different from those of the control group,and the above indexes of the TGF-β1 group were significantly different from those of the combined group(all P<0.01).The cell migration rates of mCFs in the control group,experimental-H group and CHC group were(62.60±6.50)%,(28.00±8.15)%and(39.40±4.50)%,respectively;the relative expression levels of COL1A1 protein were 1.10±0.07,0.49±0.04 and 0.34±0.06,respectively;the relative expression levels of COL3A1 protein were 1.04±0.10,0.60±0.20 and 0.37±0.03,respectively;the relative expression levels of α-SMA protein were 1.20±0.11,0.67±0.20 and 0.48±0.18,respectively;the modification levels of Pan Kla were 1.06±0.07,1.54±0.09 and 1.53±0.12,respectively;the modification levels of H3K18la protein were 0.67±0.06,1.23±0.06 and 1.14±0.08,respectively.The above indexes of CHC group and experimental-H group were significantly different from those of control group(all P<0.01).Conclusion L-lactic acid may play a role in inhibiting the fibrosis phenotype of mCFs by increasing non-histone lactic acid modification and H3K18la modification.