The images presented highlight the degree of dynamic right-to-left shunt (RTLS) across a typical patent foramen ovale (PFO) that is possible with suboptimal changes in ventilation and oxygenation that may occur under anesthesia or in the intensive care setting. In this case, a large RTLS across a PFO contributed to significant persistent hypoxemia, and the echocardiography exam was necessary for diagnosis, aggressive treatment, and complete resolution of the pathology.