HMGB1 and persistent truncus arteriosus: Moreover, CSA of cardiomyocytes were measured in mice with different treatment, and the results showed that CSA was increased in mice at 2 weeks after TAC, which was enhanced by exogenous HMGB1 treatment and attenuated by HMGB1 box A injection in myocardium, while it was up‐regulated only in TAC mice treated by HMGB1 box A at 4 weeks (Fig. 6C and E).