For hematoxylin-eosin (H&E) staining, heart tissues were fixed with 4% paraformaldehyde, dehydrated, embedded in paraffin, and then sliced to a 5-μm thickness. Paraffin slices were dewaxed with xylene, hydrated with alcohol from low to high concentrations, and then stained with H&E (Beyotime, Shanghai, China). Finally, slices were dehydrated with alcohol from high to low concentrations, made transparent with xylene, covered with a coverslip, and sealed with resin as performed previously [22 (link)]. Masson staining was performed according to the kit instructions (Solarbio, Beijing, China). H&E-stained slices were imaged using a panoramic scanning microscope (Leica, Wetzlar, Germany). For transmission electron microscopy examination, heart tissue fixation and sectioning were carried out, and a JEOL 1200 electron microscope (JEOL, Tokyo, Japan) examination was performed according to previous experimental methods [22 (link)].