Acute Pericarditis: This condition is characterized by inflammation of the pericardium, which can cause a pericardial friction rub. Electrical alternans can occur if there is a large pericardial effusion, which can lead to cardiac tamponade. The combination of these two findings strongly suggests acute pericarditis.

Cardiac Tamponade: While often a complication of acute pericarditis, cardiac tamponade can also occur due to other causes such as trauma, malignancy, or uremia. Electrical alternans is a classic EKG finding in cardiac tamponade due to the swinging of the heart within the fluid-filled pericardial sac.
Pericardial Effusion: A significant accumulation of fluid in the pericardial space can cause electrical alternans due to the heart's movement within the fluid. A pericardial friction rub may or may not be present, depending on the underlying cause and the amount of fluid.

Traumatic Hemopericardium: This is a life-threatening condition where blood accumulates in the pericardial space due to trauma. It can cause both a pericardial friction rub and electrical alternans on EKG. Prompt recognition and intervention are crucial.
Purulent Pericarditis: This condition, caused by bacterial infection of the pericardium, can lead to severe consequences if not promptly treated. While less common, it is a critical diagnosis not to miss due to its high mortality rate if left untreated.

Uremic Pericarditis: Occurring in patients with severe renal failure, uremic pericarditis can cause a pericardial friction rub and, if a significant effusion develops, electrical alternans. It is a rare but important consideration in patients with end-stage renal disease.
Malignant Pericardial Effusion: Metastatic cancer to the pericardium can cause a large effusion, potentially leading to electrical alternans. While not common, it is an important diagnosis to consider in patients with a known history of cancer.