We report on a 62-year-old man referred to the cardiac intensive care unit less than 24 hours after anterior ST-segment elevated myocardial infarction. The patient developed cardiogenic shock requiring elective intubation, vasopressor, and inotropic support. Emergency coronary angiography, revascularization, and insertion of an intraaortic balloon pump were performed. Nevertheless, the hemodynamic situation remained unstable, and a left ventricular assist device (LVAD) was inserted. Severe hypoxemia occurred several minutes after initiating the Impella Recover LD/LP 5.0 (Abiomed, Danvers, MA). Transesophageal echocardiography allowed diagnosis of patent foramen ovale. The shunt resulted from abnormal left-to-right pressure gradient due to left ventricular unloading and increased right ventricular afterload induced by mechanical ventilation. Transesophageal echocardiography was used to regulate both LVAD output and positive end-expiratory pressure settings to optimize oxygen transport. Because patent foramen ovale is common in humans, transesophageal echocardiography should be performed systematically after LVAD insertion.