CAT and diabetes mellitus: Sirius red staining of histological sections showed that cardiac‐specific overexpression of catalase dramatically ameliorated the accumulation of collagen (Fig. 1A and B, Fig. S2), and haematoxylin and eosin (HE)‐stained sections demonstrated improved myofibrillar histology, most notably in mice 8 weeks after the induction of diabetes (Fig. 1C and D, Fig. S2).