ERBB2 and Myocardial fibrosis: Disordered and loose arrangement of myocardial muscle, nucleolytic, muscle fiber rupture, and vacuolization was observed in anti‐HER2 treated mice by H&E and Masson staining, accompanied by obvious myocardial capillary congestion and myocardial fibrosis, while no obvious pathological changes were found in saline and anti‐HER2‐PCM@NP groups (Figure S30B, Supporting Information).