An x-ray image shows the chest ribs and the organs inside your chest. It makes it possible to see the heart, blood vessels, and lung fields. In infants we may be able to see the thymic gland. An x-ray may help determine if the blood flow to the lungs is normal, increased, or decreased. It also helps determine the relative size of the heart to the chest wall. An estimation of the heart size in correlation to the diameter of the chest wall is called a cardiothoracic ratio (CTR or CT ratio). This measurement will help determine if the heart is enlarged or normal in size. The chest x-ray may also pick up other abnormalities such as pleural effusion, which is an accumulation of fluid around the lungs. The diaphragm and back spine are also visualized. Patients with a congenital heart defect may have abnormalities in any of the above structures.