The pericardium has always captivated outstanding physicians from the biblical past to the current era. Early observers held romantic notions about pericardial pathology, describing fibrinous pericarditis as “hair” and associating it with a heroic death. The pericardium, a roughly flask-shaped sac that contains the heart consists of a fibrous and a serosal layer. The visceral layer is adherent to the epicardium of the heart and is thin and transparent. The outer fibrous sac is composed of collagen fibers with interspersed short elastic fibrils. The fibrous envelope extends to the great vessels as a sleeve and is continuous with the adventitia of great vessels superiorly and is attached to the central tendon of the diaphragm inferiorly. This chapter covers the congenitally absent pericardium, uremic pericarditis, recurrent pericarditis, chylous pericardial effusion, pericardial tamponade, pathophysiology, echocardiographic findings, right atrial inversion time index, right ventricular diastolic inversion, swinging heart, and Doppler findings.