Heart valve replacement. Image 1 of6. Surgeon suturing a mechanical (prosthetic) heart valve. The sutures will be used to position and hold the valve in place when it is inserted into the patient's heart. 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 the valve cannot be repaired then it must be replaced. For a sequence showing heart valve replacement see images M560/445 to M560/450.