A 70-year-old woman reported several weeks of exertional left precordial chest discomfort. Her past medical history included hypertension controlled by medication. Tc-99m sestamibi cardiac imaging revealed an abnormal area of increased activity in the anterior mediastinum. Results of a recent posteroanterior and lateral chest study were normal. A subsequent contrast-enhanced CT scan confirmed an anterior mediastinal mass, which, after sternotomy, was found to be a malignant thymoma.