Covering the heart is a sac (pericardium) that contains between 15 and 50 mL of fluid that acts as a lubricant between the 2 layers of the pericardium. There can be an abnormal increase of fluids and that can apply pressure to the heart muscle that impairs the dilation during inspiration.
Cause can be an injury of the pericardium that causes increased production of pericardial fluid. Collection of fluid in the pericardial space is called a pericardial effusion and indicates an underlying abnormality.
Infection is the leading cause of pericardial effusion. Other causes include "malignant neoplasms, infection, autoimmune disorders, kidney failure, heart failure, acute myocardial infarction, trauma, radiation exposure, inflammatory disorders, chylopericardium, dissecting aortic aneurysm, and myxedema; pericardial effusion can also be drug induced, idiopathic, or a complication of invasive procedures"
The color and consistency of pericardial fluid drained depend on the cause of the effusion.
Hope this helps provide some insight to condition, and if you have any followup questions you are welcome to respond. Thanks for the question, take care.
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