Masson’s staining showed that by 3 days post-MI, there was no significant difference in the infarct zone between WT and Klf9–/– mice (the blue area indicates fibrotic tissue and necrotic cells), but the ventricular wall of the infarcted zone of Klf9–/– mice was thinner (Figure 2, A and B); 1-week post-MI, the scar size of Klf9–/– heart was smaller (the blue area indicates fibrotic tissue), and the ventricular wall of the infarcted zone was also thinner (Figure 2, C and D). The gene discussed is KLF9; the disease is myocardial infarction.