Cor Pulmonale: This condition, characterized by right ventricular enlargement and hypertrophy due to pulmonary disease, is a common cause of right atrial enlargement. The increased pressure and resistance in the pulmonary circulation lead to right heart strain, which can cause the right atrium to enlarge.

Atrial Septal Defect (ASD): ASDs can lead to increased volume load on the right atrium, causing it to enlarge over time. This is due to the shunting of blood from the left atrium to the right atrium.
Tricuspid Regurgitation: Tricuspid valve incompetence can cause blood to flow back into the right atrium during systole, leading to its enlargement.
Pulmonary Embolism: Large or multiple pulmonary emboli can increase the pressure in the pulmonary arteries, leading to right atrial strain and enlargement.

Pulmonary Hypertension: Although not the most common cause, pulmonary hypertension is a critical diagnosis to consider, as it can lead to severe right heart failure and death if not treated promptly.
Cardiac Tamponade: Although less common, cardiac tamponade can cause right atrial enlargement due to the increased pressure exerted by the pericardial fluid on the heart.
Constrictive Pericarditis: This condition, characterized by a thickened and stiff pericardium, can impede the filling of the heart, leading to right atrial enlargement.

Ebstein's Anomaly: A congenital heart defect characterized by an abnormal tricuspid valve and right ventricular hypoplasia, which can lead to right atrial enlargement.
Carcinoid Heart Disease: A rare condition caused by carcinoid tumors secreting serotonin, which can lead to tricuspid and pulmonary valve abnormalities, resulting in right atrial enlargement.
Right Atrial Myxoma: A rare benign tumor of the right atrium that can cause obstructive symptoms and lead to right atrial enlargement.