Absence of the pericardium may be an acquired or postoperative finding, or it may be congenital. In cases where the pericardium is congenitally absent, it is the left pericardium that is most frequently deficient. This deficit may be partial or complete. In the partial variety, the left atrial appendage and pulmonary trunk are uncovered. Radiographically, these patients have a discrete bulge at these sites. Most of the patients are asymptomatic, but herniation of the cardiac structures through the partial defect can result in sudden death. Approximately 30% of patients with a congenital partial pericardial defect have some other cardiopulmonary anomaly, such as tetralogy of Fallot, patent ductus arteriosus, atrial septal defect, pulmonary sequestration, and bronchogenic cyst.

In the complete form of congenital absence of the pericardium, the cardiac silhouette is markedly displaced to the left. The main pulmonary artery is prominent, and there is interposition of lung between the aorta and pulmonary trunk, and between the left hemidiaphragm and the inferior left heart border.