What is cardiac silhouette?
Normal heart sizeThe cardiac silhouette is the most prominent central feature of the chest x-ray and it produces a familiar gourd shape with the apex of the left ventricle located just behind the left chest nipple. The inferior left ventricle wall lies on the left diaphragm and the superior base of the heart shows the aortic knob lying just to the left of the spine. A linear line descending from it, lying to the left of the spine, represents the lateral edge of the descending aorta. A normal cardiac silhouette is defined by the lower cross diameter of the heart from its right atrial boundary to the left ventricle apex occupying no more than one half the internal thoracic diameter. The right ventricular outflow tract (RVOT) at its junction with the left main pulmonary artery is concave. Note that the right hemidiaphragm is higher than the left because of the presence of the liver and not due to the weight of the heart since the same relationship occurs with dextrocardia.