Postpneumonectomy syndrome is a recognized complication following pneumonectomy, resulting from mediastinal displacement into the vacated pleural space. Mediastinal displacement causes bronchial compression and dyspnea. This report describes a 47-year-old woman who presented with shortness of breath 6 months after a left pneumonectomy. She was initially hypoxic and was found to have a patent foramen ovale. Following closure of the patent foramen ovale, she was no longer hypoxic, but she continued to have dyspnea with exertion and left lateral decubitus positioning. There was no evidence of bronchial compression, but MRI and transesophageal echocardiography suggested pulmonary vein compression due to mediastinal displacement. Transthoracic echocardiography confirmed functional pulmonary vein compression that was worse in the standing and in the left lateral positions. Her symptoms improved with mediastinal repositioning using a transesophageal echocardiography-guided approach. Positional pulmonary vein compression may be an underdiagnosed complication of pneumonectomy.