The pericardium is the double-walled sac that contains the heart and the roots of the aorta, the superior vena cava, the inferior vena cava, the pulmonary artery and the pulmonary vein. It is filled with serous fluid to allow the heart to have free movement within the cavity.
A pericardial effusion is a condition where the sac fills with fluid. If the fluid pressure interferes with the function of the heart, this is referred to as a cardiac tamponade. It can be caused by pericarditis, infection, cancer, kidney failure and other conditions. It usually presents as chest pain together with the feeling of pressure.