In total anomalous pulmonary venous return, the pulmonary veins do not return to the left atrium. In the infracardiac (meaning “below the heart”) type, the pulmonary veins drain to vessels in the abdomen with the oxygenated blood returning to the right side of the heart. The only way for blood to get to the left side of the heart is by crossing through an atrial septal defect (ASD) between the top two chambers. Sometimes the abnormal pathway that drains the pulmonary veins is too small leading to what is called “obstruction”, where the blood cannot flow normally throughout the body and babies can become very sick in these cases. Obstruction is more common with the infracardiac type.