A 78-year-old female was admitted to our hospital because of symptoms of dry cough, facial edema, and difficulty in breathing. Chest CT showed a tumor measuring 6 cm in the right upper lobe and severe stenosis of the superior vena cava. She was suspected to have lung cancer and superior vena cava syndrome. We therefore performed a lung biopsy under CT and bronchoscopy, and malignancy was also suspected, but the pathological diagnosis was inconclusive. Thereafter the tumor grew rapidly, pleural and cardiac effusion both increased, and the patient eventually died resulting from a worsening of her overall hemodynamics a month after admission. Autopsy demonstrated myocardial metastasis from pleomorphic carcinoma of the lung. It is therefore necessary to include the possibility of myocardial metastasis, as observed in this case, in the differential diagnosis because pleomorphic carcinoma has an extremely high invasive potential.