We describe the case of a 67-year-old patient, who had a stroke with subsequent right hemiparesis two years before coming under our observation. Afterwards he had no more pathological manifestation until he had sudden dyspnoea and marked cyanosis, following a prolonged immobilization due to intervention for slipped disc. Symptomatology regressed rapidly, and few hours later, the patient came under our observation in relatively fair conditions. Echocardiography evidenced moderate enlargement of right heart cavities; by subcostal view we visualized the presence of thrombotic material crossing the foramen ovale. Color Doppler showed moderate tricuspid regurgitation. Pulmonary artery systolic pressure was estimated about 55 mm Hg. The patient was immediately anticoagulated firstly by heparin, and secondly by warfarin, maintaining good clinical conditions. After a treatment of two more weeks he could be discharged with prescription of indefinite anticoagulation. Before discharge an echo examination showed the thrombus was no longer present. Pulmonary systolic pressure was estimated about 40 mm Hg. This is one of the rare cases of direct visualization of impending paradoxical embolus documented in the cardiologic literature.