Case Report: A 45-year-old male with history of alcoholism and chronic pancreatitis presented to the emergency department with chief complaint of chest pain and shortness of breath. On physical exam, he was in severe distress, with distended neck veins, distant heart sounds, and bilateral crackles on lung exam. He was hemodynamically unstable with a blood pressure of 80/60 mm Hg and pulse of 110. Pulsus paradoxus with drop in systolic blood pressure on inspiration was also observed. A noncontrast chest CT showed massive pericardial effusion. The effusion was drained urgently and a pericardial drain was left in place. Following which, his blood pressure stabilized at 110/70. Pericardial fluid analysis showed WBC of 3750/mm3 with 97% neutrophils, RBC of 59400/mm3, LDH of 1387 u/L, total protein of 4.8 g/dL, glucose 116 mg/dL, amylase 101 u/L, and lipase 196 u/L. The pericardial drain was removed the next day after decreased output. Within hours, he became hypoxic and hypotensive. CT angiogram of the chest showed reaccumulation of fluid in the pericardium along with bilateral pleural effusions. It also revealed a pancreatic pseudocyst that was found to be extending close to the posterior mediastinum and abating the posterior pericardial wall with a fistulous tract from the pseudocyst into the pericardium. He was intubated due to hemodynamic instability and moved to the ICU. He then had a ERCP followed by an EUS-guided cystogastrostomy to drain the pseudocyst. His subsequent post-op course was uneventful. Discussion: Pseudocyst formation is a common complication of both acute and chronic pancreatitis. Approximately, 40% will resolve spontaneously within 6 weeks. Extra-abdominal extension of a pancreatic pseudocyst is uncommon. Mediastinal pseudocysts result from extension of enzyme rich proteolytic fluid through the diaphragm. Most common route is via the aortic or esophageal hiatus. Rarely, it occurs by direct erosion through the diaphragm or via foramen of Morgagni. Even rarer, does a mediastinal pseudocyst penetrate into the pericardial sac. CT scan, ERCP, and magnetic resonance pancreatogram (MRP) are useful for diagnosis. The treatment modalities include (1) medical management, (2) ERCP with endoscopic pancreatic stent placement (endoscopic transpapillary/transmural technique), (3) surgery, and (4) endosonographic drainage. Conclusion: Pancreaticopericardial fistula should be considered in the differential diagnosis of pericardial effusion in a patient with known history of chronic pancreatitis and should be treated promptly.