How does the heart wear out?

Dr Mark Porter writes: "Despite its massive workload, the heart shouldn't wear out under normal conditions. But the most common problem affecting the heart is the furring up of the arteries (the coronaries) supplying the high demands of the muscular heart wall. Smoking, diabetes, lack of exercise, high cholesterol levels and poor diet all accelerate this natural process, leading to dangerous narrowing.

A heart attack occurs where a clot forms in an already narrowed section of a coronary artery, starving the muscle beyond of essential nutrients. This causes severe pain and can disrupt the natural electrical activity responsible for synchronised beats, causing the heart to become a quivering mass or stop altogether - a cardiac arrest, which leads to certain death unless normal rhythm is restored rapidly.

Less serious disturbances in the rhythm of the heart are common - hardly surprising given the complexity of the pump. Some are harmless but others can seriously interfere with the heart's efficiency. In some cases, the heart can start to fail - particularly in people with the double-whammy of high blood pressure (this increases the load on the heart wall) and restricted coronary blood flow. Symptoms include fatigue, fluid retention and breathlessness.