The heart consists of 4 pumping chambers, two on the right side which pump blood through the lungs, and two on the left which pump blood around the rest of the body. The two chambers on the left side are the

left atrium - a small, thin-walled chamber which collects the blood flowing back from the lungs 

left ventricle - which has a wall of thick muscle and is the major pumping chamber of the heart

The left ventricle has to pump large volumes of blood at high pressure and this requires a lot of oxygen, which it gets from blood vessels called coronary arteries. Oxygenated blood from the lungs returns to the left atrium and is pumped into the left ventricle. The left ventricle pumps it out through a valve into the aorta, which is the major blood vessel of the body. The first two branches of the aorta are the coronary arteries and about 5% of all the blood pumped out of the heart flows down these arteries to supply oxygen to the heart.

Normally there are two main coronary arteries, the right and the left. The left is usually the larger. The left coronary artery is only short and divides into two branches, the left anterior descending and the circumflex coronary arteries. Any of the arteries supplying blood to the heart muscle can be affected by narrowings in a process called atherosclerosis. Localised thickenings occur in the wall of the coronary arteries. These thickenings are made up of a mixture of cholesterol, calcium and other tissues. They cause two problems

1.     They decrease the cross sectional area of the coronary arteries and so act as an obstruction to blood flow and prevent sufficient oxygen getting to the heart muscle down stream from the narrowing

2.     The lining of the blood vessel becomes abnormal and this can lead to small clots forming on the vessel wall, which can lead to a sudden occlusion of the artery

These two phenomena lead to the symptoms of angina, which is when the heart muscle does not get sufficient oxygen, and heart attacks (also called myocardial infarction) when an area of heart muscle stops getting oxygen and dies. The process by which atherosclerosis leads to narrowing of the coronary arteries and causes angina and myocardial infarction is known as ischaemic heart disease.

The causes of ischaemic heart disease are not yet fully understood. Some of the things associated with ischaemic heart disease are given below. Many patients who develop angina have one or more of these features (so called risk factors) but some people have none at all.

1.     Family history - it is known that people who have close blood relatives with ischaemic heart disease are more likely to develop it themselves

2.     High cholesterol - an elevated cholesterol is associated with a high incidence of ischaemic heart disease. It is also known that by treating elevated cholesterol by modifying the diet and the use of various drugs, the risk of developing progressive angina or myocardial infarction can be decreased.

3.     High blood pressure - this again is associated with an increased incidence of ischaemic heart disease, and blood pressure above a certain threshold should always be brought under control with appropriate medications

4.     Smoking - smoking leads to the process of atherosclerosis. It also leads to the processes whereby small clots form on the thickenings in the walls of the coronary arteries. Whilst stopping smoking will not cause the narrowings already present in the coronary arteries to disappear, it will help prevent the narrowings from progressing and  will decrease the tendency of blood clots to form on the existing narrowings.