dextro-Transposition of the great arteries (d-Transposition of the great arteries, dextro-TGA, or d-TGA), is a potentially life-threatening birth defect in the large arteries of the heart. The primary arteries (the aorta and the pulmonary artery) are transposed.It is called a cyanotic congenital heart defect (CHD) because the newborn infant turns blue from lack of oxygen. [Source: Wikipedia ]