The ductus arteriosus is a blood vessel that connects the pulmonary artery (main vessel supplying the blood to the lungs) to the aorta (main vessel supplying the blood to the body). This connection is present in all babies in the womb, but should close shortly after birth. In some babies, especially in those born prematurely, this vessel may remain open. This is called a patent or persistent ductus arteriosus.
Hypoplastic left heart syndrome is a condition where the left lower pumping chamber (left ventricle) of the heart does not develop properly so is much smaller than usual. The mitral valve between the left ventricle and the upper left filling chamber (left atrium) is often closed or very small.