The heart is surrounded by a sac called the pericardium. When this sac becomes filled with fluid, the liquid presses on the heart, preventing the lower chambers of the heart from properly filling with blood, resulting in a condition called cardiac tamponade. Because the lower chambers (the ventricles) cannot fill with the correct amount of blood, less than normal amounts of blood reach the lungs and the rest of the body. This condition is very serious and can be fatal if not treated.

Blunt or penetrating injury from trauma to the chest or heart can cause large amounts of blood to fill the pericardium, resulting in cardiac tamponade. Fluid can collect inside the pericardium and compress the heart when the kidneys do not properly remove waste from the blood or when the pericardium is damaged by infection or cancer. Tamponade can also occur during open-heart surgery...