it is surrounded by a thin, double-walled fibrous sac called the pericardium. The pericardial sac contains about 30 milliliters of a transparent fluid called pericardial fluid. The pericardium does many things—it lubricates the heart, allowing it to continue pumping while expending the least amount of excess energy. The pericardium also shields the heart from infections that might occur in the tissues around the heart. Unlike the heart, which floats like a fetus in its sac, the pericardium is attached to the tissues and bones around it, effectively anchoring the heart in place, which would
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