Cyanosis in atrial septal defect typically occurs when pulmonary hypertension develops. Platypnea-orthodeoxya is an uncommon syndrome, still under debate, characterized by breathlessness and arterial oxygen desaturation exacerbated in the upright position. An interatrial communication is a common finding in this syndrome, but the absence of a right to left pressure gradient complicates the physiopathological picture. To explain the right to left shunt, it is generally advocated a concomitant condition that alternates the sterical relationship between inferior vena cava orifice and the atrial septal defect. A case of a 58-year-old male with platypnea-orthodeoxya syndrome related to a fenestrated redundant interatrial septum without any additional pathologic condition is reported. Possibly, this isolated anatomical abnormality could lead to a right to left shunt in the absence of other coexisting predisposing factors. It is reasonable to hypothesize the septum secundum bulging like a 'spinnaker' into the right atrium, so that it deviates the inferior vena cava venous blood towards the left atrium. Echocardiographic evaluation is mandatory to achieve a correct diagnosis and to decide the therapeutic strategy.