The heart is split into four parts. Two collecting chambers at the top called Atria and two pumping chambers at the bottom called Ventricles. Single ventricle circulation is a broad term describing rare heart abnormalities in which the lower part of the heart has only one working pumping chamber. This is usually because one of the inlet valves has failed to develop normally. This results in the mixing of the oxygenated 'red' and deoxygenated 'blue' blood and problems with the way blood is delivered to the lungs and to the rest of the body. Surgery will always be required but it will not be possible to fully correct the heart.