Now, what exactly does that mean? Well, because some of that blood from the systemic circulatory system moves back into the pulmonary trunk, less of the oxygen will actually reach the tissues of that individual. And as a result, that heart will need to pump harder and more to actually make sure that the tissues get enough oxygen. So, PDA, or patent ductus arteriosis, causes oxygenated blood to move from the high pressure a order and into the low pressure pulmonary trunk. And this means less oxygen will reach the tissues of that individual. What it also means is more blood will actually flow into the lungs, because if this oxygenated blood is mixing with the deoxygenated blood, the influx of blood into the pulmonary system will be greater.