Pericardial effusion is the abnormal accumulation of fluid in the space of the pericardium, the double-layered membrane surrounding the heart. This condition can arise due to a wide range of underlying causes. Possible reasons include infections, cancer, heart failure, kidney failure, autoimmune or inflammatory diseases such as rheumatoid arthritis, hormonal disorders, trauma, or medical procedures. Additionally, the accumulation of blood in the pericardial space or obstruction of pericardial fluid drainage can also lead to effusion.