What forms the borders of the heart on the frontal PA or AP chest X ray?
The chest radiograph represents an important first step in the imaging workup of cardiovascular disease. On a PA frontal view of the chest, a cardiothoracic ratio (cardiac width : thoracic width) of less than 1 : 2 is considered normal in adults. Analysis of the cardiac silhouette can yield valuable information about chamber enlargement. The right atrium comprises the right heart border. This border becomes bulbous when the right atrium is enlarged. Superiorly, three convexities (called the “three moguls”) comprise the left heart border, which, from superior to inferior, are the aortic knob, main pulmonary artery, and left atrial appendage. Inferiorly, the left ventricle (lateral wall and apex) comprises the left heart border.