Paradoxical embolism refers to the embolic entry of a venous thrombus into the systemic circulation through a right-to-left shunt. Impending paradoxical embolism, in which a venous thrombus extends from the right atrium through a patent foramen ovale (PFO) into the left atrium, is usually diagnosed with echocardiography. The most common cause of paradoxical embolism through a PFO is the acute pulmonary embolism. We report a case of a 78-year-old woman with acute pulmonary embolism, complicated by impending paradoxical embolism.