The functions of Kv1.1 channels in ventricles were explored for the first time revealing that Kv1.1‐deficient mice exhibit resistance to pacing‐induced arrhythmias with isoproterenol, echocardiographic contractility deficits, and underlying action potential prolongation without evidence of structural or channel expression remodeling. Here, KCNA1 is linked to cardiac arrhythmia.