Objectives Extracorporeal shock wave (SW) therapy ameliorates cardiac remodeling after acute myocardial infarction (AMI). However, it remains to be examined whether and how SW therapy ameliorates myocardial fibrosis after AMI. Fibrocytes are associated with myocardial fibrosis. Thus, we examined whether SW therapy ameliorates myocardial fibrosis and whether fibrocytes are associated after AMI in pigs.Materials and methods AMI was created by coronary embolism. Twenty-five pigs were divided into three groups: AMI+SW group (AMI with SW therapy, n=15), AMI group (without SW therapy, n=5), and sham+SW group (SW therapy without AMI, n=5). The collagen area fraction was examined by Masson's trichrome staining. The presence of fibrocytes was identified by immunofluorescence and confocal microscopy. The location of CXCL12 was examined by immunohistochemistry.Results Compared with the AMI group, the AMI+SW group showed significantly ameliorated myocardial fibrosis in terms of collagen area fraction (27.21 +/- 8.13 vs. 10.13 +/- 4.96, P<0.05) and reduced fibrocytes (CD34/-smooth muscle actin: 35.40 +/- 11.72 vs. 12.27 +/- 7.71, P<0.05; CXCR4/-smooth muscle actin: 40.80 +/- 8.96 vs. 16.54 +/- 6.38, P<0.05). There were positive correlations between the collagen area fraction and the number of fibrocytes (r=0.936; P<0.05) and between the number of CXCR4(+) fibrocytes and the SDF-1/CXCL12(+) cells (r=0.802; P<0.05) in the three groups.Conclusion The results show that SW therapy ameliorates myocardial fibrosis after AMI in pigs, which is associated with the decreased amount of fibrocytes.