Activating κ-OR was reported to reduce the area of myocardial infarction and to relieve arrhythmia caused by ischemia-reperfusion injury, inhibiting myocardial cell apoptosis and promoting cardiac functions, which indicated that the function of κ-OR is correlated with regulation of Ca2+ level [25, 26]. The gene discussed is OPRK1; the disease is cardiac arrhythmia.