Shortness of breath after pneumonectomy is a common finding that has multiple causes. We report the cases of two patients with shortness of breath on assuming an upright posture (platypnea) that followed pneumonectomy; these individuals developed right-to-left shunt across a patent foramen ovale (PFO) with normal right-sided intracardiac pressures. Both contrast echocardiography and magnetic resonance imaging (MRI), including a recently introduced dynamic ultrafast imaging technique, proved helpful in diagnosing this condition noninvasively.