A thick muscular wall called the |septum| divides the |heart| lengthwise into the left and right sides. The two sides do not interact with each other; rather, each pumps ~blood~ separately. The left side of the |heart| pumps bright oxygen-rich ~blood~ into the main |artery|, the |aorta|, and is distributed to a network of ~blood~ vessels throughout the body. The ~blood~ passes its oxygen on to the tissues of the body and returns through the |veins| into the right side of the |heart|. From there, it is pumped to the |lungs| to be replenished with oxygen and returned to the left side of the |heart|.
Before birth, an opening known as the |foramen ovale| in the |septum| allows oxygen from the mother to flow directly from the right to the left atrium, bypassing the lungs which do not function until the moment of birth. The |foramen ovale| normally closes at birth, but occaisionally it remains open, resulting in poorcirculation through the |lungs| where it fails to take up enough oxygen, causing the skin of the new-born child to turn blue. This condition is known as a hole in the |heart| and can often be repaired by surgery.
