The pericardium is a membranous sac, divided into a fibrous layer and a serous layer, which is further divided into a visceral layer and a parietal layer. The visceral layer covers the surface of the heart, the parietal layer adheres to the fibrous layer, and there is a cavity in between called the pericardial cavity. Normally, the parietal layer is very smooth, and the presence of a pericardial friction rub indicates the onset of inflammation. Inflammation causes exudate to flow into the pericardial cavity, creating an accumulation known as pericardial effusion.
