Remember in normal fetal circulation the _______ allows blood to shunt from the pulmonary artery to the aorta. The effects of a _______ are dependent upon the pulmonary vascular resistance (PVR) and system vascular resistance (SVR). Normally at birth these two pressures are nearly equal and shunting is minimal. As the PVR decreases, SVR remains unchanged thus blood moves from the aorta to the PA, which is a left to right shunt. This increases the amount of blood in the pulmonary artery thus increasing pulmonary blood flow, which in turn increases the amount of blood returned to the left side of the heart. This increases the work of the left side of the heart. A reversal of the shunt may occur if pulmonary hypertension develops from increased blood flow through the pulmonary artery. If this happens deoxygenated blood will enter the aorta below the level of the subclavian artery causing the child to be cyanotic in the lower portion of their body but normal in the upper body.