Abnormal heart sound Pericardial friction rub 2023-06-12T13:19:02Z A pericardial friction rub is a grating, to-and-fro sound that occurs in phase with the heart sounds. Pericardial friction rubs can be differentiated from pleural friction rubs because they occur independently of breathing. A pericardial rub is highly specific for acute pericarditis. It is generally heard over the left sternal border, it is often louder at inspiration but sometimes can be better heard on forced expiration while the patient bends forward. In most cases, the rub is triphasic (audible in atrial, ventricular systole, and ventricular diastole phases) and is of high frequency. Cardiac rub