There are four major heart valves that control blood flow through the heart. If the valves become narrow (stenosis) so that blood flow through them becomes difficult, or leaky so that some blood flows in the wrong direction, they may need to be repaired or replaced. Valves may be damaged by diseases such as rheumatic fever or bacterial infection, degenerate with age or may not be formed properly at birth.

Heart valve surgery involves making a cut through the front of the chest and breastbone (sternotomy) to expose the heart. The heart is then stopped and its function taken over by a heart-lung machine. Part of the heart is then opened and the valve repaired or possibly replaced using a human donor valve, a valve from a pig or cow or an artificial valve. The heart is then restarted, the heart-lung machine disconnected and the breastbone closed with wires. The operation usually takes between three and five hours.