Coloured X-ray of a 78-year-old male patient with a prosthetic aortic valve being placed by percutaneous aortic valve replacement. This is a minimally invasive procedure, where an artificial (prosthetic) heart valve is delivered via a catheter rather than through an incision in the chest. There are four valves in the human heart, all of which prevent the backflow of blood. Damage to the valves can lead to malfunctioning of the heart and death. If a valve cannot be repaired it must be replaced.