The heart is basically a big muscle which pumps blood around the body. Like all your muscles, the heart needs oxygen to work. This oxygen is brought to the heart by blood flowing through the coronary arteries.
The right and left coronary arteries branch off the aorta — the large main blood vessel which leaves the heart with fresh oxygen-rich blood.
If the coronary arteries become narrowed by fatty deposits in the lining of the arteries (atherosclerosis) then the flow of blood to the heart muscle may be restricted. If the heart muscle doesn't get enough blood it doesn't get enough oxygen to work properly — this is called ischaemia.
Ischaemia can cause chest pain or discomfort (angina), often described as a feeling of pressure or tightness in the chest. Angina pain may also be felt in the neck, shoulders or arms. Angina is often brought on by physical activity, and typically improves with rest.
2. Mayo Clinic. Coronary artery disease. Last updated 29 June 2012. http://www.mayoclinic.com/health/coronary-artery-disease/DS00064 (accessed Feb 2013).
3. National Heart, Lung and Blood Institute. What is angina? Updated June 2011. http://www.nhlbi.nih.gov/health/health-topics/topics/angina/ (accessed Feb 2013).