Pericardial tamponade, also known as cardiac tamponade, is a medical condition caused by the compression of the heart due to a build-up of fluid, blood, or air in the pericardium, which is the double-walled sac surrounding the heart. Normally, the pericardium is filled with a small amount of fluid that prevents the two layers of the pericardium from rubbing together as the heart beats. Pericardial tamponade occurs when there’s an increased amount of fluid, blood, or air inside the pericardial sac. This leads to pressure on the heart and prevents it from expanding properly. As a result, less blood is pumped out with each heartbeat, decreasing the blood supply available to the rest of the body. Pericardial tamponade can rapidly progress to circulatory shock and even cardiac arrest. Thus, it is considered a medical emergency that requires prompt treatment.