We describe a case of a patient with polycystic kidney and liver disease presenting with a 4 year history of shortness of breath. This was caused by a liver cyst pressing on the inferior vena cava, right atrium and ventricle, leading to a right to left shunt across a patent foramen ovale. This is consistent with the condition Orthodeoxia Platypnoea, which occurs when desaturation and dyspnoea occur in the upright position in association with an intra atrial shunt.