A condition in which some of the deoxygenated blood in the lungs does not come into contact with air, and full gas exchange does not take place.
A condition in which blood, by going through an abnormal pathway or bypass, does not travel its normal route. It may occur when an arteriovenous fistula forms or in congenital anomalies of the heart in which the blood passes from the right atrium or ventricle directly to the left atrium or ventricle respectively, through a defect in the wall (septum) that normally separates the atria and ventricles.