Of all the conditions that can afflict the heart, pericarditis is among the most unpredictable and least-understood. But in many cases, its a short-term, self-limited problem that can be cleared up with anti-inflammatory medications. Surgery may be needed to treat constrictive pericarditis. Pericarditis is an inflammation of the pericardium, the thin, two-layered sac that surrounds the heart to help protect it from infection. Many circumstances can lead to pericarditis, ranging from a viral infection to a reaction to a heart attack or heart surgery to autoimmune diseases. Allan Klein, MD, Director of Cardiovascular Imaging Research and Director of the Center for the Treatment and Diagnosis of Pericardial Diseases at Cleveland Clinic, says that in developed nations like the U.S., the cause of about 80 percent of pericarditis cases are idiopathic (unknown) in origin or viral. Often the cause isnt found.