In a healthy person enough blood is able to reach the heart muscles via the coronary arteries. However, if this supply is disrupted the cells in the heart muscle don’t receive enough oxygen and glucose to be able to function properly which can cause the tissue to die. If a blockage occurs in a coronary artery this affects larger amounts of muscles cells which can result in a serious heart attack.

Most blockages are caused by a blood clot, otherwise known as a thrombus, by a process called thrombosis. When a blood clot forms in a coronary artery this is known as coronary thrombosis.

However, the clot may not have formed in the coronary artery but, instead, have been transported via the blood stream from another part of the body. In this case it’s known as an embolus and the actual blockage is called an embolism.

The chances of thrombosis are increased by atherosclerosis. This is when fatty deposits settle in the arteries and the artery walls themselves thicken, a condition known as antheroma. The results are that the lumen decreases in size and the walls lose their elasticity so that less blood can flow through them. This in turn leads to blood clots.

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The process of the formation of atherosclerotic plaque is as follows:

• Lipoproteins transport cholesterol around the body.
• Too much cholesterol causes it to leak out from the lipoproteins.
• This is then deposited on the walls of the arteries.
• White blood cells become trapped in the cholesterol.
• Free radicals are released which causes the arterial wall to become damaged.
• This activates blood platelets which stick to the damaged areas and release clotting factors known as thromboxanes.
• A plaque is formed.
• If this is ruptured then it forms a thrombus.
• Once released into the bloodstream it becomes an embolus.
• It’s now free to travel through the circulation. If it ends up in the brain it can cause a stroke, in the lungs it can lead to a pulmonary embolism, and in to the coronary arteries it can cause a heart attack.

When the coronary arteries become narrowed and damaged by atherosclerotic plaques this leads to coronary heart disease. As the lumen decreases, more pressure is required to move the blood through the vessels and an increase in blood pressure leads to further damage.

Atherosclerosis can also cause angina: it’s hard for the blood to pass through the narrow vessels but the cells don’t die as some blood still manages to reach the heart. However, there’s still a shortage of blood reaching the heart muscle and, during physical activity, this causes chest pains.