Pericardial effusion occurs when too much fluid builds up around the heart.
The heart is surrounded by a double-layered, sac-like structure called the pericardium. The space between the layers normally contains a very small amount of fluid.
But if the pericardium is diseased or injured, the resulting inflammation can lead to pericardial effusion. Fluid can also build up around the heart without inflammation. Sometimes, pericardial effusion can be caused by the accumulation of blood after a surgical procedure or injury.
When the amount of fluid exceeds the pericardium's "full" level, pericardial effusion puts pressure on the heart, causing poor heart function. If left untreated, pericardial effusion can cause heart failure or even death.