Histological findings of radiofrequency ablation lesions. (a) Hematoxylin and eosin (HE) staining myocardial slices showed local changes, normal myocardium (control), tissue ablation with saline (saline group) and ablation with NPs treatment (P/B-COS NPs), acute bleeding, and tissue injury adjacent to the ablation line. (b) In the enlarged view (red dotted bordered rectangle in (a)) of the local reversible injury site after ablation, there was more obvious inflammatory cell recruitment in the saline group. (c) Transverse (enlarged view of the black dotted bordered rectangle in (a)) and (d) longitudinal sections of myocardium at normal myocardium and ablation site of local irreversible injury. There was significant hematoma in the saline group.