Originally Posted by mrsD

I believe the most common cause is infectious, followed by autoimmune.

Here is a link:
http://en.wikipedia.org/wiki/Pericardial_effusion

One of my son's teachers in high school, continued exercise while he had a virus and developed this severely, and almost died as a result. Otherwise healthy, and only 42 yrs old.

There are mild forms and acute forms. That is basically all I know about it, as one really needs a doctor to carefully follow you if you show effusion tendencies.