A 62-year-old asymptomatic woman was found to have a left pulmonary artery filling defect on a contrast computerized tomography scan of the chest. Workup revealed a diagnosis of left pulmonary artery sarcoma. Pulmonary artery sarcomas are rare tumors with poor prognosis. A high index of clinical suspicion is required to make a timely diagnosis and avoid inappropriate treatment for pulmonary embolism.