Introduction

Transposition of the great arteries (TGA) is a rare, severe heart condition where the two main arteries leaving the heart are reversed. 

The heart is made up of:

• left and right atrium – the top two chambers
• left and right ventricle – the bottom two chambers
• pulmonary artery – a passage that carries blood from the right ventricle to the lungs 
• aorta – a passage that carries blood from the left ventricle to the rest of the body
• coronary arteries – passages that carry blood into the heart.

In a normal heart, blood travels through the body in the following steps:

1. the right ventricle pumps blood through the pulmonary artery into the lungs to get oxygen
2. oxygen-rich blood travels back from the lungs into the left atrium, then down to the left ventricle
3. the left ventricle pumps the oxygen-rich blood out to the rest of the body through the aorta.

In babies born with TGA, the position of the arteries is switched. This means:

• the pulmonary artery is connected to the left ventricle, sending oxygen-rich blood back to the lungs
• the aorta is connected to the right ventricle, sending oxygen-poor blood through the body.

When this happens, oxygen-rich blood cannot get through the body properly. 

TGA is a congenital heart condition. This means it is something your baby is born with.

TGA is life-threatening and needs to be corrected with surgery within the first few weeks of life.

Babies who are born with TGA may have symptoms like:

• difficulty breathing
• cyanosis - blue or grey colour in the skin
• a weak pulse or heartbeat
• heart murmur – a swishing sound in the heart
• poor feeding and weight gain.

TGA can be diagnosed:

• during pregnancy with an ultrasound that looks at the structure of the baby’s heart
• after your baby is born.

Symptoms of TGA can look like other conditions. A specialist doctor will look at your baby and order tests and scans to check the heart's structure and how it works.

Tests and scans can include:

• pulse oximetry - a probe placed on your baby’s finger or toe to measure the level of oxygen in the blood
• chest x-ray – to see the size and shape of the heart and lungs
• electrocardiogram (ECG) – a test that records the heart's electrical activity and shows abnormal rhythms and heart muscle stress.
• echocardiogram (echo) – a scan that uses sound waves to take a moving picture of the heart and heart valves
• cardiac catheterisation – a thin tube is guided through a vein in the groin, up into the heart, and then used to get information about the structures inside.

TGA must be treated with surgery within the first few weeks of a child’s life.