MODEL RELEASED. Heart valve repair surgery. Surgeon threading an artificial support for the a heart valve is being threaded into place. This patient has a weakened mitral valve, found between the heart's left upper (atrium) and lower (ventricle) chambers. The sutures (threads) here are different colours in order to facilitate tying off once the support is securely in place. There are four valves in the human heart, all of which prevent the backflow of blood. Damage or weakening of the valves can lead to malfunctioning of the heart and death. If the valve cannot be repaired then it must be replaced.