Transposition of the Great Arteries (TGA) is associated with several different arrangements of heart anatomy, so is not one condition. The common feature is that the connections between the heart and main arteries (the aorta carrying blood to the body, and the pulmonary artery carrying blood to the lungs) are abnormal.
In this form of TGA the main arteries are connected so that the aorta receives low oxygen ('Blue") blood from the right sided heart pump (the right ventricle) and the pulmonary artery receives high oxygen ("pink") blood from the left sided heart pump (the left ventricle). This is the reverse of usual, and the result is very low oxygen blood returning from the body and being pumped back to the body without the chance to pick up oxygen rich blood. Babies would not survive if it were not for naturally occurring pre-birth communications (the ductus arteriosus which is a pre-birth connection between aorta and pulmonary artery, and the foramen ovale which is a pre-birth window in the wall between the atria the low pressure collecting chambers inside the heart) staying open for a little while after birth.
Early treatment is directed at maintaining oxygen levels at a safe (if not normal) level, sometimes by giving Prostaglandin ( a drug modelled on natural hormones) to keep the ductus arteriosus open. Sometimes this does not, by itself, increase the oxygen levels to a "safe" zone, and a procedure called a balloon atrial septostomy is needed. This is a specialist procedure carried out only by paediatric cardiologists, and involves a catheter (fine hollow tube) being passed from the umbilical vein or a leg vein in the groin, to the inside of the heart where a small balloon attached to the catheter is filled with fluid and drawn across a naturally occurring curtain of tissue covering the foramen ovale inside the atria. If successful this will tear the curtain tissue and improve the mixing of pink and blue blood so oxygen levels in the body can increase enough to be "safe" for the baby. All these measures are temporary ways to stabilise the baby until surgery is possible.
Surgery is usually carried out in the first 2 weeks of life and is called an "arterial switch", where the arteries are relocated to the correct side of the heart, and the tiny coronary arteries nourishing the muscle of the heart are also moved so they stay connected to the arty coming from the left ventricle. After surgery the heart works very much like normal, with a normal sequence of blood flow, and normal oxygen levels to the body circulation. After surgery the arteries remain in a somewhat unusual position relative to each other, but this and the function of the heart and valves are part of the surveillance process that follows on into life. This is a major, open heart procedure and uses the heart lung machine to assist the surgeon.
Children generally live a normal quality of life after successful surgery, can generally participate in all sports, and rarely require further surgery.
This is a similar condition to "simple" TGA (described above) but also has a ventricular septal defect (VSD) present - a hole in the wall between the two ventricles. Treatment may be similar to "simple" TGA. although the VSD needs to be closed as part of the switch operation unless there are other complicating features. The outcomes are also similar.
There are a range other complex forms of heart abnormality where TGA forms part. Sometimes this involves narrowing in the path of blood flow to the lungs. Sometimes the anatomy inside the heart can also be very different to normal. Treament for these conditions will often differ a great deal from "simple" TGA, although the final surgical solutions can provide excellent functional results in most children.
There is a different condition called L-TGA (or congenitally corrected transposition of the great arteries) usually with "ventricular inversion". This is a very different condition to TGA, and although the names are similar (which can cause confusion), the clinical journey and treatment is very different.