It has been shown that injection of the nonselective OR agonist β‐endorphin into perfusion solution caused only atrial fibrillation and atrioventricular block in isolated rat heart.260, 261 It should be noted that in vivo β‐endorphin exhibits antiarrhythmic properties in anesthetized cats with coronary artery occlusion.262 In 1987, Lee and Wong demonstrated that injection of the preferential κ OR agonist dynorphin1‐13 (20 μg/heart) caused both atrial and ventricular arrhythmias in isolated rat heart.263 This effect was antagonized by naloxone. Here, OPRK1 is linked to Ventricular arrhythmia.