Pericardial effusion is a buildup of fluid in the space between the heart and the sac around the heart (pericardium).
The extra fluid can be caused by many things. Some causes are pericarditis (inflammation of the sac), heart attack, surgery, kidney failure, infection, some cancers, and certain diseases such as lupus. Sometimes the cause is not known.
If the fluid buildup is gradual and the heart is tolerating the increased fluid around it, treatment of the underlying cause may be tried first. In some cases, the fluid might need to be drained.