The authors report the case of myocardial infarction occurring immediately after rapid intravenous infusion of a high dose of corticosteroids prescribed for a relapse of multiple sclerosis. Ventriculography confirmed the myocardial damage but the coronary arteries were normal. An aetiological investigation was negative. The authors review the cardiac secondary effects which may be very serious and even fatal. Coronary insufficiency is rare (only 3 previously published cases); it is therefore difficult to determine the prognosis. The possible mechanisms of infarction are discussed. Finally, the authors underline the importance of recording an ECG before treatment, of ECG monitoring during the infusion, and the need for repeating the recordings and of prolonging hospital admission when necessary.