Heart valves function by opening and closing over a billion times during a lifetime. This requires plasticity of the valve cells (interstitial and endothelial cells) and the valve extracellular matrix. Diseased valves are replaced by human donor, bioprosthetic or mechanical valves. For children born with defect valves, only human donor or mechanical valves are used although neither can grow with the growing child heart. Furthermore, activation of the immune system can cause valve rejection and early valve degeneration. In this project, I test the dynamic culture of human donor valves in attempts to increase valve vitality and growth potential. Furthermore, I test lentiviral gene delivery to achieve immune evasion and prevent valve rejection.