Definition of Total anomalous pulmonary venous return:

Total anomalous pulmonary venous return is a congenital heart disease (present at birth) in which none of the four veins that take blood from the lungs to the heart is attached to the left atrium (left upper chamber of the heart).

Causes, incidence, and risk factors:

The cause of total anomalous pulmonary venous return (TAPVR) is unknown.

In normal circulation, blood is sent from the right ventricle to pick up oxygen in the lungs. It then returns through the pulmonary veins to the left side of the heart, which sends blood out through the aorta, and around the body.

In TAPVR, oxygenated blood returns from the lungs back to the right atrium or right ventricle -- instead of the left side of heart. In other words, blood simply circles to and from the lungs and never gets out to the body.

If the infant is to live, a large atrial septal defect (ASD) or patent foramen ovale (passage between the left and right atria) must exist to allow oxygenated blood to flow to the left side of the heart and rest of the body.

The severity of this condition depends on whether the pulmonary veins are obstructed. There are four subtypes of TAPVR, based on the location of the veins' connection back to the heart. In one type, the veins run into the abdomen, passing through a muscle (diaphragm). This muscle squeezes the veins and narrows them, causing the blood to back up into the lungs. This type causes symptoms early in life.