Hardened arteries

The build-up of cells, fat, cholesterol and other substances - together known as plaque - in the arteries can lead to blood flow being blocked, preventing supply to the heart and brain.

The inner walls of the arteries become narrow because of a build-up of plaque, causing hardening known as atherosclerosis.

It is a slow, progressive disease which may begin in childhood. Why it starts is unknown but it may be due to high cholesterol and triglyceride levels in the blood, high blood pressure and smoking.

Deposits build up on the artery wall, and may stimulate the cells in the wall to produce further substances adding further layers of blockage.

Fat builds up around and within these cells causing narrowing, or stenosis.

Thickened

Dr Tony Gershlick, consultant cardiologist and honorary senior lecturer at Leicester University, said: "One way of looking at it is as if the coronary arteries are bits of hollow spaghetti.

"If you look at one 2 or 3cm portion of that spaghetti where the wall has thickened, then the amount of blood you can get down that spaghetti is reduced."

The inner layer of the artery wall thickens considerably, reducing the blood flow and starving the heart and/or brain of oxygen. A blood clot can also form, blocking off the artery completely.

The arteries of the leg are often affected, as well as abdominal arteries and those near the pelvis - iliac arteries. This is called peripheral arterial disease.

Pain

The first sign of peripheral arterial disease is pain in the calf muscles, thighs or buttocks when walking or exercising. As it progresses, the pain may become continuous and prevent sleeping.

Narrowing of the arteries supplying blood to the heart can cause angina or heart attack.

Blockage of arteries to the neck can interfere with the flow of blood to the brain and may cause stroke. If untreated, gangrene of the leg can result.

Dr Gershlick added: "It is to some extent a disease of ageing. Many people over the age of 60 will have some degree, irrespective of risk factors, of coronary artery narrowing."

Risk factors include smoking, high cholesterol levels, diabetes and obesity. Family history and high blood pressure are also implicated and a combination of factors worsens a person's chances of developing atherosclerosis.