## Results and Discussion
### Effects of pDMYO- and pDSIS-Gels on Acute Myocardial Infarction in Rats  
As shown in Figure 5A,B, LVEF and LVFS in pDSIS-gel, pDMYO-gel and PBS groups were significantly decreased, suggesting that the cardiac function of rats was significantly deteriorated due to myocardial infarction. The values of LVEF and LVFS in hydrogel groups were higher than those in PBS group, but the results were nonsignificant, indicating that the material may have a positive effect on improving the rat heart function. H&E staining (Figure 5C) showed that, compared with the sham group, the left ventricular cavity in PBS group was significantly enlarged and there was local collapse. The structure of the ventricular wall in the myocardial infarction area in PBS group was destroyed, and the ventricular wall became thinner, with a minimum thickness of 0.5 mm. The left ventricular cavity was smaller and the ventricular wall were thicker in pDSIS-gel and pDMYO-gel groups than that in PBS group. In pDMYO-gel group, the wall thickness was 1.3 mm. The local magnified H&E-stained images (Figure 5D) showed that the myocardial matrix in the infarct border area of pDMYO-gel and pDSIS-gel groups was more uniform and denser than that of PBS group, and there were more microvessels in the infarct border area of pDMYO-gel and pDSIS-gel groups. Masson staining images (Figure 5E) showed that a large amount of collagen fibers (blue colour) was deposited in the myocardial infarction area. The length of infarction area in the hydrogel group was shorter than that in the PBS group, and the fibrosis level in the pDMYO-gel group was the lowest. The local magnified Masson-stained images of the infarct border area (Figure 5F) showed that there were less collagen fibers (blue colour) in pDMYO-gel group than that in PBS and pDSIS-gel groups.  
Figure 5: Effect of decellularized matrix hydrogels on acute myocardial infarction in rats (**A**) the effect of decellularized matrix hydrogels on left ventricular ejection fraction (LVEF). (**B**) the effect of decellularized matrix hydrogels on left ventricular shortening fraction (LVFS). (**C**) The H&E staining images of the rat heart sections (0.7 times magnification, the scale bar is 2000 \(\upmu\)m); (**D**) The local magnified H&E-stained images of the infarct border area (18 times magnification, the magnified area is the blue box area in Figure 5C; the yellow arrow marks the location of the vessel; the scale bar is 100 \(\upmu\)m); (**E**) the Masson staining images of the rat heart sections (0.7 times magnification, the scale bar is 2000 \(\upmu\)m); (**F**) the local magnified Masson-stained images of the infarct border area (10 times magnification, the magnified area is the blue box area in Figure 5E. The collagen fibers were blue color, while the myocardial fibers were red color and the cell nuclei were blue black. The scale bar is 200 \(\upmu\)m). * denotes statistical difference within the same group with \(p<0.05\), respectively (\(n=3\)).  
The above results indicate that pDMYO-gel has a better effect on improving cardiac function, inhibiting myocardial fibrosis, and maintaining ventricular wall thickness after acute myocardial infarction in rats, which is consistent with the results of cell culture study in vitro that pDMYO-gel is more conducive to maintaining myocardial cell viability.