Anomalous left coronary artery (ALCAPA) is a heart defect in which the left coronary artery (which carries blood to the heart muscle) is connected to the pulmonary artery instead of to the aorta.

ALCAPA is present at birth (congenital).

An anomalous left coronary artery is a problem that occurs when the baby's heart is developing, early in the pregnancy. The developing blood vessels in the heart do not connect correctly.

In the normal heart, the left coronary artery starts in the aorta -- the major blood vessel that takes oxygen-rich blood from the heart to the rest of the body.

In children with ALCAPA, the left coronary artery starts at the pulmonary artery -- the major blood vessel that takes oxygen-poor blood from the heart to the lungs.

When the left coronary artery starts in the pulmonary artery, it carries oxygen-poor blood to the left side of the heart. When the heart does not get enough oxygen, it begins to die, a condition leading to a heart attack in the baby.

A condition known as "coronary steal" further damages the heart in babies with ALCAPA. The low blood pressure in the pulmonary artery causes blood from the abnormal left coronary artery to flow toward the pulmonary artery instead of toward the heart. This results in less blood and oxygen to the heart, which will also lead to a heart attack in a baby. Coronary steal develops over time in babies with ALCAPA if the condition is not treated early.