Tricuspid atresia is an abnormal development of the right side of the heart. It includes a missing valve between the upper and lower chamber and a smaller than normal lower chamber. Tricuspid atresia can make it difficult for your heart to efficiently pump blood to the lungs to get oxygen. Some may also have holes in the wall between the left and right side of the heart. The holes allow oxygen-rich and oxygen-poor blood to mix.

Heart Chambers and Valves
heart anatomy
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Blood Flow Through the Heart
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Tricuspid atresia develops when the baby is in the womb. It is not known exactly why some hearts develop this way.