In the forward position the side contours
In the forward position, the lateral contours of the cardiovascular shadow have two arcs on the right and four on the left. On the right contour, the lower arch is well defined, which corresponds to the right atrium; the upper slightly convex arch is located medially to the lower one and is formed by the ascending part of the aorta and the superior vena cava. This arc is called vascular. Above the vascular arch a small arc is still visible, going up and outwards, towards the clavicle; it corresponds to the brachiocephalic vein. Below the arc of the right atrium forms an acute angle with the diaphragm. In this corner, with a low standing of the diaphragm at the height of a deep breath, one can see a vertical shadow strip that corresponds to the inferior vena cava.
On the left contour, the uppermost (first) arc corresponds to the arc and the beginning of the descending part of the aorta, the second to the pulmonary trunk, the third to the left ear and the fourth to the left ventricle. The left atrium, located for the most part on the posterior surface, is not kraeobrazuyuschy with dorsoventral rays and therefore not visible in the anterior position. For the same reason, the right ventricle located on the anterior surface is not contoured, which also merges with the shadow of the liver and diaphragm below. The place of transition of the left ventricular arch into the lower contour of the cardiac silhouette is marked radiographically as the apex of the heart.
In the area of the second and third arcs, the left contour of the heart silhouette has the character of indentation or interception, which is called the “waist” of the heart. The latter separates the heart from the vessels connected with it, which constitute the so-called vascular bundle.
Turning the subject around the vertical axis, one can see in oblique positions those segments that are not visible in the anterior position (right ventricle, left atrium, most of the left ventricle). The most widely used are the so-called first (right nipple) and second (left nipple) oblique positions.