Two separate parallel blood streams arise due to the sinus venosus and the AV canal shifting to the right, and the formation of the inferior vena cava. The aortic stream originates from the inferior vena cava and flows from the right into the left atrium. From the left atrium, it flows through the left part of the AV canal into the left ventricle, and is expelled through the part of the outflow tract that develops into the aorta. The pulmonary stream flows from the superior vena cava into the right atrium, and is situated ventrally to the aortic flow. It flows from the right atrium through the right part of the AV canal to reach the right ventricle, where it winds ventrally around the aortic stream and travels along the part of the outflow tract that becomes the pulmonary trunk (truncus pulmonalis). It enters the aorta through the ductus arteriosus. Part of the pulmonary stream is later fed to the left atrium through the developing lungs (animation: development of the endocardial tube).