Patent foramen ovale (PFO) is a congenital abnormality present in 25%-30% of healthy adults and rarely leads to any sequelae. It is associated with a left-to-right shunt which usually does not lead to any haemodynamic compromise. Occasionally, the shunt can get reversed; that is, right-to-left shunt occurs due to worsening pulmonary hypertension and can lead to persistent hypoxia. It is rare for the shunt reversal to happen in the absence of pulmonary hypertension. Here, we present an exceedingly rare case in a 61-year-old man presenting with hypoxia, was found to have shunt reversal due to unilateral diaphragmatic paralysis. He was successfully treated with PFO closure. The purpose of this report is to consider rare possibilities of PFO shunt reversal when the right-sided heart pressure is normal and to highlight that a simple chest X-ray can be a clue to the diagnosis.