Enlargement of the heart (cardiomegaly) can be caused by various cardiac diseases, including congestive heart failure, hypertension, pulmonary embolism and diseases, such as renal failure and anemia. In subtle cases, the cardiothoracic ratio can be calculated by dividing the maximal horizontal thoracic diameter by the maximal horizontal heart diameter on a PA chest radiograph. A ratio greater than 0.50 indicates enlargement of the cardiac silhouette which can be related to cardiomegaly, pericardial effusion or large epicardial fat pad. Specific cardiac chambers may be enlarged, particularly the left atrium. Left atrial enlargement may be manifested by a “double density sign”, concave appearance of the left heart border, or splaying of the carina