The heart is divided into four chambers that help circulate blood through the body. The top two chambers are called atria. The bottom two chambers are called ventricles. Two valves are between the upper and lower chambers. Tissue called the septum divides the chambers. The tissue grows as the fetus develops.

An atrioventricular septal defect is present at birth. It occurs when any of the tissues that divide the septum do not grow completely. This leaves one or more holes. It may also leave one leaky valve instead of two separate valves.

This condition is caused when the septal tissue fails to grow correctly as the fetus develops in the womb.

Ventricular Septal Defect
Ventral septal defect
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