Well, remember at birth, as we mentioned earlier, there is a reversal in pressure taking place. And so the pressure on the right side of the heart is lower than the pressure on the left side of the heart. And what that means is the pressure inside the systemic circulatory system is higher than the pressure inside the pulmonary circulatory system. So what do we have at birth? So basically, the ductus arteriosis does not close. Yet we have a higher pressure inside the order, which is part of the circulatory system, than inside the pulmonary trunk, which is part of the pulmonary circulatory system.