What is pericarditis?

Pericarditis is caused by inflammation or infection of the pericardium, the thin sac (membrane) that surrounds the heart. There is a small amount of fluid between the inner and outer layers of the pericardium. Often, when the pericardium becomes inflamed, the amount of fluid between its two layers increases, causing a pericardial effusion. If the amount of fluid increases quickly, the effusion caused can impair the ability of the heart to function properly. This condition is called pericardial tamponade.