Pulmonary Artery Leiomyosarcoma is a very rare neoplastic disease that simulates a PTE; ECHO and CT have shown themselves inadequate in diagnosing this pathology while cardiac MRI has allowed to exclude a PTE and to diagnose solid lesion. The lack of response to conservative therapy, the atypicalness of the radiological framework, should cause suspect of this disease. Diagnosis in the shortest possible time is necessary because the surgical treatment, especially in the case with extended lesions, must be early.