Tong et al. showed that administration of the κ-OR agonist U50,488H after myocardial ischemia and reperfusion can combat the occurrence of arrhythmias, reduce myocardial cell necrosis and apoptosis, inhibit the inflammatory response after reperfusion, and exert a direct protective effect on the myocardium. Here, OPRK1 is linked to cardiac arrhythmia.