Although myocardial stunning occurs in coronary artery disease, it has rarely been reported with hyperthyroidism. A 72-year-old woman presented with general weakness, shortness of breath and febrile sensation of 10 days duration. The serum thyroid hormone level was elevated. Serial EKGs showed significant ST elevation suggesting transmural ischemia, but coronary angiography was not significant. Echocardiography showed regional wall motion abnormality of apical hypokinesia, which was improved after medication for hyperthyroidism. We report this case as an example of myocardial stunning associated with hyperthyroidism. (Korean Circulation J 2004; 34(5):516-519)