As in papillary muscle dysfunction complicating mitral prolapse, dyskinesis of the left ventricular wall underlying the papillary muscles has been shown to cause mitral regurgitation following myocardial infarction. Myocardial stunning has been experimentally evidenced to cause mitral regurgitation due to a wall motion abnormality, but it has not yet been clinically defined. We report a clinical case of transient severe mitral regurgitation complicating myocardial stunning caused by coronary vasospasm. Transient wall motion abnormality beneath the anterolateral papillary muscle was considered to be responsible for the mitral regurgitation.