Abnormal ST T‐wave changes can be found at presentation in various noncoronary disorders; misinterpretation of these patterns as ischemic heart disease can lead to erroneous diagnosis and treatment. Here we present a case of myasthenia gravis (MG) with thymoma, in which the resting electrocardiogram (ECG) led to a misleading diagnosis of myocardial ischemia. After thymectomy, the ECG resumed a normal pattern. Myasthenia gravis is not usually considered in the differential diagnosis of conditions associated with an abnormal ECG. The combination of dysphagia, dyspnoea, ECG changes, and creatine kinase (CK) elevations may easily bring to mind an erroneous and possibly deleterious diagnosis of myocardial ischemia. Copyright © 2009 Wiley Periodicals, Inc.