The postoperative TNM stage was T3N1M0 (3.5 × 3.5 × 1.5 cm, pT3, Ly1, v3, p3[diaphragm], pm0, br+, n+), and radiation therapy was given (total, 51 Gy). After treatment, the patient had no symptoms and signs suggestive of a recurrence of lung cancer. A physical examination performed at the time of hospital admission revealed a BP of 138/88 mm Hg and a heart rate of 36 beats/min. A systolic murmur (Levine II/VI) was heard at 3 on the left sternal border. Lung auscultation revealed attenuated respiratory sounds in the lower right side. Laboratory tests showed the following: WBC count, 13,100 cells/μL; BUN concentration, 31 mg/dL; creatinine concentration, 2.3 mg/dL; aspartate aminotransferase concentration, 340 IU/L; alanine aminotransferase concentration, 397 IU/L; lactate dehydrogenase concentration, 898 IU/L; creatine kinase concentration, 346 IU/L; and C-reactive protein concentration, 10.4 mg/dL. A chest radiograph showed a right pleural effusion (Fig 1
, top left, A). An ECG showed atrioventricular (AV) dissociation (Fig 1, top right, B). On echocardiography, a large mass (2.1 × 4.9 cm) was noted in the basal area of the ventricular septum that extended to the left ventricular lumen (Fig 1, bottom left, C); ventricular contractility was preserved, although the mitral inflow pattern revealed an abnormal relaxation pattern. Additionally, during systole, the tip of this mass extended toward the aortic valve, resulting in increased left ventricular outflow tract (LVOT) velocity (2.2 m/s). A thoracic CT scan revealed a low-density mass located on the ventricular septum (Fig 1, bottom right, D).