Collection of fluid in a body cavity is an effusion. It is called a transudate if there are few cells and/or protein. If this fluid is protein-rich and/or has many cells within it, then it becomes an exudate. The large amount of fibrin in such fluid can form a fibrinous exudate on body cavity surfaces. Here, the pericardial cavity has been opened to reveal a fibrinous pericarditis with strands of stringy pale fibrin between visceral and parietal pericardium.