Pericarditis is an inflammation of the two layers of the thin, sac-like membrane that surrounds the heart. This membrane is called the pericardium; thus the term pericarditis means inflammation of the pericardium.

Pericarditis is fairly common. It affects approximately one in 1,000 people. The most common form is caused by a viral infection. People in their 20s and 30s who have had a recent upper respiratory infection are most likely to be affected, along with men aged 20-50. One out of every four people who have had pericarditis will get it again, but after two years these relapses are less likely to occur.

The viruses that cause pericarditis include those that cause influenza, polio, and rubella (German measles). In children, the most common viruses that cause pericarditis are the adenovirus and the cocksackievirus (which is most likely to affect children during warmer weather).

Although pericarditis is usually caused by...