Acute Pericarditis: This is the most common cause of a pericardial friction rub. It is characterized by inflammation of the pericardium, which can be due to various causes such as viral infections, uremia, or post-myocardial infarction. The presence of a pericardial friction rub is a hallmark of acute pericarditis.

Myocardial Infarction with Pericarditis: Myocardial infarction can lead to pericarditis, especially if it involves the epicardium. A pericardial friction rub may be heard in these cases.
Uremic Pericarditis: Patients with chronic kidney disease or those undergoing dialysis can develop uremic pericarditis, which may present with a pericardial friction rub.
Post-Cardiac Surgery Pericarditis: Pericarditis can occur after cardiac surgery, and a friction rub may be audible.

Pulmonary Embolism with Pericardial Involvement: Although less common, a pulmonary embolism can lead to pericardial involvement, presenting with a friction rub. Missing this diagnosis could be fatal.
Aortic Dissection: An aortic dissection can extend to involve the pericardium, leading to a friction rub. This is a medical emergency that requires immediate attention.
Cardiac Tamponade: While not always associated with a friction rub, cardiac tamponade is a life-threatening condition that can result from pericardial effusion. It is crucial to consider this diagnosis in the appropriate clinical context.

Sarcoidosis: Sarcoidosis can involve the pericardium and lead to a friction rub, although this is a rare manifestation of the disease.
Lupus Pericarditis: Systemic lupus erythematosus (SLE) can cause pericarditis, which may present with a friction rub. This is a less common cause but should be considered in patients with a history of SLE.
Tuberculous Pericarditis: In areas where tuberculosis is prevalent, tuberculous pericarditis should be considered as a rare cause of a pericardial friction rub.