We describe the development and exacerbation of protein-losing enteropathy after relocating to an environment at an altitude of 3695 feet in El Paso, Texas, in a patient who had undergone a Fontan operation. This report should heighten awareness to the possibility of such patients developing protein-losing enteropathy at high-altitude, with hypoxemia-induced pulmonary vasoconstriction, and subsequent elevation of central venous pressure, the most likely underlying mechanism.