Children with Down Syndrome are often born with heart problems that requires complex surgery. Before we can do surgery on a baby’s heart, we need to know that their lungs are strong enough to cope with the operation. For some babies with Down Syndrome, we find that their lungs do not work as well as they could. In Our Lady’s Children‘s Hospital, Crumlin, we take a piece of the lung (while the baby is given an anaesthetic) and look at it under a microscope to see if the lungs look healthy enough for a surgery. There isn’t much guidance to tell us if looking at a piece of the lung tells us important information or not. We want to review the charts of all babies in our hospital, with Down Syndrome, who had a piece of their lung examined to see if the test is correct in telling us which babies with Down Syndrome should have complex heart surgery or not. This will help us in deciding what care is best for babies with Down Syndrome not just in our hospital but for everyone who cares for babies with Down Syndrome who need heart surgery.