As the Truncal Valve is directly above the Ventricular Septal Defect, blood is pumped from both the right and left ventricles (RV and LV) to the lungs and to the body. The mixing of oxygen-rich and oxygen-poor blood reduces the efficiency of the circulatory system.

Pulmonary (lung) resistance is lower than systemic (body) resistance. Therefore, there is usually increased blood flow to the lungs. This increased pulmonary blood flow can lead to congestive heart failure. These infants have rapid breathing, irritability, difficulty feeding and gaining weight.

Because the lung arteries are connected to the high pressure pumping chambers (ventricles) there is high blood pressure in the lung arteries. If the lungs are exposed to both high pressure and extra blood flow for an extended time (months to years), irreversible pulmonary hypertension can occur.

Truncus Arteriosus can also be associated with DiGeorge syndrome.  A genetic syndrome caused by a chromosomal microdeletion (22q11).  Children with DiGeorge syndrome can have other non-cardiac problems such as cleft palate and poor feeding.  This complicates their care and recovery.