Taking a step towards a major goal in heart valve prosthetics, scientists have created an adaptable heart valve replacement that can be expanded over time as the heart grows. The artificial valve safely worked in growing young lambs for a period of up to 10 weeks. Although studies with longer follow-up times are needed to further validate the design, the device could offer a superior alternative to traditional, fixed-diameter heart valve prostheses that cannot grow along with a child's heart. More than 1.35 million children worldwide are born with a congenital heart disorder each year, resulting in an annual expense of around $6 billion. Of these disorders, most that involve heart valves are treated with prosthetic replacements. But children with these valves must undergo up to five invasive open-heart surgeries to replace their valves before reaching adulthood, leaving them at risk of stroke, hospital stays and even death. To provide a more permanent solution that reduces surgical burden, Sophie Hofferberth and colleagues created a heart valve that draws inspiration from valves in human veins, which can expand and contract to handle large changes in blood flow volume. Their valve is composed of two synthetic leaflets attached to a stent and can be manually expanded with a balloon catheter to accommodate larger volumes of blood moving through the heart. When implanted into four young lambs and four adult sheep, the prosthetic valves showed good performance without impeding blood flow. In a separate test in seven other lambs, the valves remained functional for 10 weeks without causing injury or major inflammation. The scientists caution that longer-term animal studies should assess the valve's durability and effects on the heart, as well as the structural integrity of the expandable leaflet design.