This report describes the case of a young woman who presented to an emergency department with severe abdominal pain and shock. The patient was found to have pericardial tamponade due to a massive pericardial effusion. On further evaluation, the etiology of this effusion was considered to be secondary to hypothyroidism with concominant acute viral pericarditis leading to a fulminant tamponade. The presentation, differential diagnosis, and management of pericardial effusion and tamponade secondary to hypothyroidism and viral pericarditis are discussed. The diagnosis of hypothyroidism in conjunction with acute viral pericarditis should be considered in patients presenting with unexplained pericardial effusion and tamponade.