Pericardial effusion refers to the accumulation of fluid in the sac surrounding the heart. It is a medical condition that can lead to health complications if left untreated. Different terminologies are used to describe pericardial effusion, including cardiac tamponade, fluid in the pericardium, pericardial fluid, and pericardial sac effusion. Cardiac tamponade is the most severe condition of pericardial effusion, where the fluid accumulation compresses the heart and obstructs its function. A pericardial rub is another synonym for pericardial effusion, referring to the noise produced when the inflamed pericardium rubs against the heart during contraction. Other synonyms for pericardial effusion include heart bag fluid, water around the heart, and pericarditis with effusion.