Truncus arteriosus (TA) is a rare congenital cardiovascular anomaly characterized by a single arterial trunk arising from the heart by means of a single semilunar valve (<I>i.e.</I> truncal valve). Pulmonary arteries originate from the common arterial trunk distal to the coronary arteries and proximal to the first brachiocephalic branch of the aortic arch. TA typically overrides a large outlet ventricular septal defect (VSD). The intracardiac anatomy usually displays situs solitus and atrioventricular (AV) concordance.

A reduction in the amount of air transported into the pulmonary alveoli by breathing, leading to hypercapnia (increase in the partial pressure of carbon dioxide).