In the most basic sense there are two sides to the heart. The left side is strong and muscular. It takes oxygenated 'red' blood from the lungs and pumps it to the aorta, a very big artery that takes blood to head and body. The right side is more flexible but not as strong. It takes the waste 'blue' blood' coming back from the body and pumps this through the pulmonary artery back to the lungs to be recycled. In some babies the two pipes (Aorta and Pulmonary Artery) have been switched around. This is not good. It means blue blood coming back from the body to be recycled in the lungs cannot get there. Instead it is getting pumped straight back round the body again. Equally the red blood coming back from the lungs cannot get to the body and instead (wastefully) gets sent back to the lungs. This situation is known as Transposition of the Great Arteries. It absolutely requires urgent surgery in babies. HOWEVER! sometimes nature has also swapped the umping chambers over. In this situation the pipes have been swapped but so have the pumping chambers. The result is that blood flows normally from lungs to body and back to the lungs again. Sadly the situation is far from perfect. This rare defect is often associated with other defects, rhythm problems such as heart block and remember the flexible right pumping chamber was never designed to spend a whole life pumping to the head and body. It is not always strong enough for this.