Cardiac tamponade is a serious but uncommon condition characterized by excessive fluid in the pericardium (the sac surrounding the heart). Normally, the pericardium contains about 25 milliliters of this pale, yellow fluid. The fluid insulates and protects the heart. It also limits the outward movement of the heart’s chambers atria and ventricles.

However, too much fluid building up in the pericardium (from blood or other fluids leaking into the sac) puts pressure on the heart muscle, decreasing the heart’s ability to fill with and circulate blood. Cardiac tamponade that occurs rapidly is known as acute cardiac tamponade. This may be the result of a sudden injury or surgical complication. It is a medical emergency that must be addressed immediately.

Cardiac tamponade that occurs more slowly is known as subacute cardiac tamponade. This may be the result of a disease such as cancer. The condition can sometimes be treated with medication aimed at reducing the quantity of fluid in the pericardial sac. If there is a possibility of it worsening into acute tamponade, however, it must be treated with surgery or possibly other less invasive techniques.

Although these conditions are treated similarly, they differ in the amount of fluid necessary to cause symptoms of tamponade. Acute cardiac tamponade can be caused by the rapid infusion of 200 milliliters (ml) of fluid into the pericardium. Subacute cardiac tamponade may be caused by as much as 2000 ml because the pericardium is able to stretch and accommodate more fluid. Symptoms of subacute cardiac tamponade may be similar to heart failure (e.g., breathlessness, distended neck veins).