[en] Intrathoracic, extracardiac abnormalities were detected in 12 of 210 patients who underwent Tc-99m red blood cell gated cardiac blood pool (GCBP) study. The abnormalities include absent pulmonary perfusion due to tumor mass, compression in five, pleural effusion in four, pneumothorax in two, and left lung mass attenuation in one. These abnormal findings were confirmed with concurrent or subsequent chest radiography or chest CT. Patients with intrathoracic great vessel abnormality (such as aneurysm), pericardial effusion, and a splenomegaly were excluded. Although pulmonary or thoracic wall lesions are not frequently seen, the incidental finding during GCBP study shall lead to further study for such clinically unsuspected lesions, which may benefit the patient's care