In normal circulation, the pulmonary artery comes out of the right ventricle and the aorta comes out of the left ventricle, which are separate from each other.
With truncus arteriosus, a single artery comes out of the ventricles. There is usually also a large hole between the two ventricles (ventricular septal defect). As a result, the blue (without oxygen) and red (oxygen-rich) blood mix.
Some of this mixed blood goes to the lungs, and some goes to the rest goes of the body. Often, more blood than usual ends up going to the lungs.
If this condition is not treated, two problems occur:
- Too much blood circulation in the lungs may cause extra fluid to build up in and around them, making it difficult to breathe.
- If left untreated and more than normal blood flows to the lungs for a long time, the blood vessels to the lungs become permanently damaged. Over time, it becomes very hard for the heart to force blood to them. This is called pulmonary hypertension, which can be life-threatening.