Pericardial friction sounds are mainly seen in acute pericarditis, which is an acute inflammatory disease of the pericardial visceral and mural layers, with viral infections being the most common cause. In the acute phase of acute pericarditis, the inflammation of the pericardium causes fibrin exudation from the pericardial visceral and mural layers, which can result in roughness of the inner surfaces of the pericardial visceral and mural layers, causing pericardial friction during cardiac systole and diastole. Pericardial friction is the most diagnostic sign of acute pericarditis. It is a scratchy, rough, high-frequency sound, mostly located in the precordial area, and is most pronounced in the 3rd and 4th intercostal spaces at the left edge of the sternum. Pericardial friction sounds can last for hours, days, or even weeks. When a pericardial effusion occurs the visceral and mural layers separate, and the friction sound disappears.