A case of positionally symptomatic right-to-left shunting across a patent foramen ovale with both platypnea and orthodeoxia despite normal pulmonary arterial pressures and normal right ventricular function is documented. When the patient was in a supine position, the calculated right-to-left shunt was 12.8 percent, and when seated 25 percent. Surgical closure of the patent foramen ovale relieved the symptoms and positionally induced shunting. The prevalence and associations of permanent and intermittent patency of the foramen ovale are discussed. It is recommended that those at risk of thromboembolism be screened for patency by contrast ultrasound or color flow techniques. If present, surgical closure needs to be considered to prevent paradoximal embolism and stroke.