A cyanotic heart defect is any congenital heart defect (CHD) that occurs due to deoxygenated blood bypassing the lungs and entering the systemic circulation, or a mixture of oxygenated and unoxygenated blood entering the systemic circulation.
It is caused by structural defects of the heart such as right-to-left or bidirectional shunting, malposition of the great arteries, or any condition which increases pulmonary vascular resistance.
The result may be the development of collateral circulation.
Presentation includes the following:[citation needed]