We evaluated a case of a 36 - year - old women with a mass inside a pulmonary artery lumen diagnosed after she had transiently lost consciousness. Such a clinical manifestation of intimal sarcoma, a tumor of the great vessels, has not been described so far. Tumor masses are often misinterpreted as a thrombus and that is why a diagnosis of pulmonary embolism is made. PET has raised some hopes of distinguishing these two disorders. Intimal sarcoma is characterized by an extremely poor prognosis and thus a proper diagnosis and urgent surgical treatment should be implemented promptly.