IL2 and cardiac arrhythmia: Cardiac side effects are common with IL-2 therapy and range from sinus and supraventricular tachycardia to cardiomyopathy and myocarditis; however, most side effects appear to be reversible with discontinuation of therapy.1,2 In this article, we report a case of a patient who developed myocarditis and near-lethal arrhythmia after receiving high-dose IL-2 therapy.