The complete circulation:

One-way flow

Blood must flow one way only through the circulatory system. Valves in the heart, aorta and veins ensure this one-way flow.

Closure of a valve prevents back flow.

Faulty heart valves

Heart valves may become faulty. A valve may not:

• open as wide as it should, restricting blood flow through the heart - this means less blood reaches the body, pressure builds up and the lungs can swell with fluid
• close properly and allow blood to leak back through into the atrium

A patient will not always have symptoms. A scan of the heart can diagnose the problem. When symptoms are present, these are shortness of breath, dizziness, rapid heart rate and chest pain. The problem can lead to heart failure.

If the condition is severe, the patient will require surgery.

Faulty heart valves can be replaced:

• with a biological valve from a human donor or made from animal tissue from a pig or cow
• with a mechanical valve made from strong, durable materials

The operation is usually successful. Mechanical valves last longer, but blood can clot on them. A patient may need long-term medication that prevents blood clots developing. Biological valves are more likely to wear out.

Listen to a podcast about the circulatory system with Dr Alex Lathbridge.

Listen to the full series on BBC Sounds.