Background: The extracardiac Fontan arose as an alternative in order to prevent the classical procedure's sequelea. Complications of the extracardiac Fontan have been described, but this case report aims to highlight the devastating and infrequent complication of external conduit compression. Methods and Results: A 25-year-old male underwent Fontan conversion to extracardiac Fontan for atrial arrhythmias and giant right atrium. He developed postoperative respiratory distress, renal failure, and hemorrhagic pancreatitis, which prompted CT scans of his chest and abdomen that demonstrated external compression of the conduit by mediastinal hematoma. Endovascular stenting restored flow through the conduit, but the patient ultimately expired. Conclusions: External Fontan compression, which can be caused by numerous sources, may lead to significant organ dysfunction and can be difficult to recognize despite invasive monitoring. We report this complication and suggest ringed conduits to be considered to avoid the possibility of external compression.