When the proliferative activity of fibroblasts was measured, using 5-ethynyl-2′-deoxyuridine (EdU) or immunodetection of Ki-67 after myocardial infarction, the fibroblasts with proliferating activity appeared two to four days after myocardial infarction (active fibroblasts), and the conversion of fibroblasts to myofibroblasts occurred four to seven days after myocardial infarction [27]. Here, MKI67 is linked to myocardial infarction.