This is a type of congenital heart defect in which there is a single blood vessel arising from right and left ventricles instead of normally two blood vessels (Pulmonary Artery and Aorta ). 

There is always a large Ventricular Septal Defect allowing mixing of the blood completely and producing blueness. This defect leads to excessive blood flow to the lung and eventually the pressure in the Pulmonary Arteries increases dangerously leading to a condition called pulmonary hypertension. This can be life threatening. There are three varieties of truncas defect depending on specific branching pattern of the single trunk.

Lethargy, poor feeding, fatigue, bluish discoloration and delayed growth.

An echocardiogram clinches the definitive diagnosis.

Banding of pulmonary artery coming off truncus may be necessary initially. Complete total correction may be attempted once pulmonary artery pressure comes down. Complete repair affords good result but re operation may be necessary.