We report 5 cases of acute heart failure (AHF) related to multiple sclerosis (MS) relapses. AHF was inaugural in 3 patients, always preceded or accompanied by signs of brainstem dysfunction; it was severe, requiring intensive care management. Echocardiography showed left ventricular hypokinesis. No other cause of AHF has been found. All patients showed a new medullary lesion on brain magnetic resonance imaging. All had rapid and complete recovery of ventricular function after intravenous corticosteroids. We concluded that the cases represent a takotsubo phenomenon. Physicians should be aware of rare cases of takotsubo cardiomyopathy in MS relapses. Ann Neurol 2017;81:754–758