Constrictive pericarditis: Scarring of the pericardial sac. This limits the ability of the heart to function because it cannot expand enough to collect blood and pump it to the lungs and then back to the body. Bleeding into the pericardium from trauma or from a heart operation is the most common cause of constrictive pericarditis, but tumors or infections can also be the cause. The constriction occurs slowly over time and causes shortness of breath on exertion and a decreased ability to exercise. Swelling in the legs and the abdomen may exist because it is difficult for blood to return to the heart, and fluid leaks out into the tissues. Pericardotomy, an operation to split open the pericardium to free up the constriction around the heart, may be required to improve function.