GJA1 and cardiac arrhythmia: Our research mainly aims to compare DOX with methylprednisolone (MP), which enhances MMP activity and inhibits inflammatory reactions, and to observe 1) the effect of DOX on MMP activity in the myocardium after myocardial infarction and its effect on the distribution of Cx43, and 2) the effect of DOX on the susceptibility of rats to arrhythmia in a myocardial infarction model.