Patent foramen ovale is a persisting communication between the left and right atrium, present in approximately 25% of population, usually asymptomatic. Under normal conditions there is either no blood flow or a hemodynamically nonsignificant left-to-right shunt between the atria. However, increased right atrium pressure, as it is in pulmonary embolism, can make PFO a right-to-left shunt and poses a risk of paradoxical systemic embolism, including the risk of ischemic stroke. Here we report a case of a patient presenting with venous thromboembolism provoked by a recent polytrauma. We identified a large thrombus stuck in patent foramen ovale - an impending paradoxical embolism. Both surgical intervention and systemic thrombolysis were contraindicated so the patient was administered an anticoagulation treatment with unfractionated heparin and warfarin. By frequent echocardiography we were able to monitor complete resolution of the thrombus by 6 months from the diagnosis, with no systemic embolism.