Paradoxical embolism occurs when a venus-source thrombus passes through an intracardiac defect or pulmonary shunt into the systemic circulation. Depending on the site of the resultant embolization, it can cause stroke, peripheral arterial occlusion or visceral organ ischemia. A patent foramen ovale (PFO), a common remnant of fetal circulation present in about 25% of the general population, is the most frequent cause of R-L shunt in adults. It has been associated with stroke of unclear cause (cryptogenic, CS) that accounts for approximately 25–40% of all ishemic strokes. PFO occurs in 40–56% of patients <55 years old with CS or transient ischemic attack (TIA). However, approximately one third of discovered PFOs represent incidental findings. The possibility of paradoxical embolism should be considered in all patients with an arterial embolus of non-identifiable source. The diagnosis can be difficult to establish and multidisciplinary approach is usually necessary to exclude other possibilities from the differential diagnosis. Treatment options for secondary stroke prevention include risk factor modification, antithrombotic or anticoagulant therapy and endovascular or surgical closure of PFO. The choice is dependent on the risk of stroke recurrence, the benefit/risk ratio between antithrombotic therapy and surgery, as well as the potential complications of each intervention. To decide if endovascular closure is indicated, it is essential to determine the degree of causal relationship between the PFO and the CS. Patients with high “PFO-attributable recurrence risk“ are most likely to benefit from percutaneous PFO closure.