Normal “Three vessel view”. The “three vessel view” refers to a view of the great vessels in the superior mediastinum. The main pulmonary artery (MPA) may be seen passing directly posterior where it meets the arterial duct, which connects to the descending aorta. The transverse aortic arch meets the duct to form a V shape. To the right of the aortic arch there is the circular cross-section of the superior vena cava. Note that the trachea is seen in this projection and normally lies outside the V formed by the transverse aortic arch and the arterial duct