Heart of an infant, heart organ at birth At birth, the cardiovascular system changes from placental circulation to autonomic circulation. The foramen ovale between the right atrium and the left atrium closes around the age of 4 months. While the arterial duct between the aortic arch and the pulmonary trunk closes around the third week. It is then called an arterial ligament. It is shown in white. Then the venous ligament of Arantius to the left of the inferior vena cava closes and becomes the venous ligament of the liver. The black arrows represent the direction of blood flow in the newborn heart. Blue and red colors indicate oxygenation of the blood. Blue represents deoxygenated blood and red represents oxygenated blood.