Abstract
Introduction: The prevalence of patent foramen ovale (PFO) is around 25% of the general population and constitutes about 95% of all right-to-left intracardiac shunts. In most cases never causes a health disturbance, but sometimes is associated with paradoxical embolism. It usually occurs in combination with pulmonary thromboembolism, which suddenly increases the right heart pressure, favouring thrombus displacement. The risk of paradoxical embolization (PE) may be increased by the presence of the two most common genetic risk factors for venous thrombosis: factor V Leiden (G1691A) and prothrombin (PT) G20210A.
The detection of thrombus passage throw PFO allows the definitive diagnosis of paradoxical embolism, but as it is a transient phenomenon, it was rarely described in the literature.
Case Report: A 29-year-old Syrian woman was admitted to the emergency department, referring to chest pain, dyspnea and palpitations, of sudden onset. With a previous illness history of stroke at age 18 and obesity. She was followed up in a Neurology consultation, where a prothrombin gene mutation (G20210-A) was diagnosed and medicated with acetylsalicylic acid. Chest CT angiography was performed, which documented bilateral pulmonary thromboembolism and it was identified a large thrombus crossing the foramen ovale in a transthoracic echocardiogram. Anticoagulation with unfractionated heparin was started and she was later transferred to the cardiothoracic surgery department.
Conclusion: In this case, we highlight the coexistence of genetic and structural risk factors, which culminate in a rare case of pulmonary thromboembolism with atypical presentation of large thrombus crossing the foramen ovale, with potential for pulmonary and systemic embolization.

Key words: patent foramen ovale, paradoxical embolism, prothrombin G20210A, pulmonary thromboembolism, thrombus