A normal heart (left) and one affected..

The interior of the heart is composed of valves, chambers, and associated vessels


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The external structures of the heart include the ventricles, atria, arteries and veins. Arteries carry blood away from the heart while veins carry blood into the heart. The vessels colored blue indicate the transport of blood with relatively low content of oxygen and high content of carbon dioxide. The vessels colored red indicate the transport of blood with relatively high content of oxygen and low content of carbon dioxide.


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An atrial septal defect is a congenital heart defect where the wall between the right and left atria does not close properly, leaving a hole between the two atria.


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A normal heart (left) and one affected by atrial septal defect. The defect is a hole in the wall that separates the chambers of the heart, resulting in the mixing of oxygenated and unoxygenated blood. (Illustration by GGS Information Services.)