Pericardial effusion is the buildup of extra fluid in the space around the heart. If too much fluid builds up, it can put pressure on the heart. This can prevent it from pumping normally.
A fibrous sac called the pericardium surrounds the heart. This sac consists of two thin layers. Normally, there is a small amount of fluid between them. The fluid reduces friction between the two layers as they rub against each other during each heartbeat. In some cases, extra fluid can build up between these two layers leading to a pericardial effusion.
A little fluid won’t cause much of a problem. But if too much fluid builds up, it can make it hard for the heart to expand normally. This condition is called cardiac tamponade. It usually requires emergency treatment. Because the heart can't expand normally, less blood can enter the heart from the body. This can reduce the amount of oxygenated blood going out to the body. But not all pericardial effusions cause cardiac tamponade.
In some cases, pericardial effusion develops quickly. This is known as acute pericardial effusion. Other times, the fluid builds up slowly. This is known as subacute pericardial effusion. Chronic pericardial effusion occurs when cardiac effusion happens more than once over time