Partial anomalous pulmonary venous return, sometimes called partial anomalous pulmonary venous connection, is a heart defect present at birth (congenital) in which some of the pulmonary veins carrying blood from the lungs to the heart flow into other blood vessels or into the heart's upper right chamber (right atrium), instead of correctly entering the heart's upper left chamber (left atrium). This causes some oxygen-rich blood from the lungs to mix with oxygen-poor blood before entering the right atrium.

This defect is due to some of the pulmonary veins incorrectly attaching to the heart's right atrium or other blood vessels, instead of connecting to the left atrium as they normally do.

Some people with this defect also have a hole between the upper heart chambers (atrial septal defect), which allows blood to flow between the upper heart chambers (atria).

People with this condition may also have other congenital heart defects.