Aortopulmonary septal defect
The aortic window is a normally radiolucent region below the aortic arch. It is formed by the bifurcation of the trachea and traversed by the left pulmonary artery. It is visible in the left anterior oblique radiograph of the heart and great vessels. It can play a role in the identification of enlarged lymph nodes. Its borders are the left atrium, vertebral column, and aortic arch.