Foetal heart. Heart of a 7-month-old foetus. The foetal heart develops from a single heart tube. By seven weeks of age it has divided into the four- chambered structure seen in adults, but the normal flow of blood through the heart does not begin until birth. Whilst the foetus is developing, it obtains oxygen from the placenta, an organ attached to the lining of the uterus where its blood mixes with that of its mother. As a result, its circulatory system bypasses the lungs, and oxygenated blood from the placenta is pumped to different areas of the body by the heart. The blood is returned to the placenta when fully deoxygenated.