Heart attack explained

A heart attackThe death of a section of heart muscle caused by an interruption in its blood supply. Also called a myocardial infarction. is the death of a section of heart muscleTissue made up of cells that can contract to bring about movement. as a result of its bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. supply being cut off. This condition is sometimes called a myocardial infarctionDeath of an area of heart muscle due to poor blood supply., with the word 'myocardial' meaning heart muscleTissue made up of cells that can contract to bring about movement., and 'infarction' meaning death of a piece of tissue because of a lack of oxygen.[1]

Blood clots

Heart attacks are almost always caused by a bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. clot forming within a coronaryRelating to the arteries supplying the heart itself. arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood., one of the arteries that supply the muscleTissue made up of cells that can contract to bring about movement. of the heart. Usually, the clot forms because fatty deposits called plaqueAny flat, raised patch; for example, a raised patch on the skin, fatty deposit in the inner wall of an artery, or layer over the surface of a tooth. build up in the arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood. wall, a process known as atherosclerosisDisease leading to fatty deposits in the inner walls of the arteries, which reduce and may eventually obstruct blood flow., and a plaqueAny flat, raised patch; for example, a raised patch on the skin, fatty deposit in the inner wall of an artery, or layer over the surface of a tooth. then ruptures or wears away.[1]

Atherosclerosis is often referred to as 'furring up' of the arteries. In the heart this is known as coronaryRelating to the arteries supplying the heart itself. arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood. disease, although atherosclerosisDisease leading to fatty deposits in the inner walls of the arteries, which reduce and may eventually obstruct blood flow. is actually a progressive disease that affects all of the arteries in the body, not just the arteries that supply the heart.

Atherosclerosis in the coronaryRelating to the arteries supplying the heart itself. arteries may not cause any symptoms, or may lead to a range of conditions affecting the heart, including anginaA central chest pain caused by insufficient oxygen supply to the heart.  - chest pain caused by insufficient bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. flow to the heart - and heart attackThe death of a section of heart muscle caused by an interruption in its blood supply. Also called a myocardial infarction.. Severe symptoms from unstable anginaChest pain caused by poor blood supply to the heart that comes on unpredictably - not just during exercise. or myocardial infarctionDeath of an area of heart muscle due to poor blood supply. can be difficult to tell apart, a condition known as acute coronary syndromeA range of clinical conditions caused by coronary artery disease: it encompasses the full spectrum from unstable angina to heart attack..

Other causes

The formation of a clot blocking the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. supply to the heart is not the only cause of a heart attackThe death of a section of heart muscle caused by an interruption in its blood supply. Also called a myocardial infarction., or myocardial infarctionDeath of an area of heart muscle due to poor blood supply..

Other possible causes may include spasm of the coronaryRelating to the arteries supplying the heart itself. arteries, which will also restrict the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. supply to the heart. One possible reason for coronaryRelating to the arteries supplying the heart itself. arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood. spasm is cocaineA narcotic drug extracted from coca leaves. use. Cocaine causes the coronaryRelating to the arteries supplying the heart itself. arteries to constrict while increasing the oxygen demand of the heart, by increasing the heart rate and bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. pressure.[2]

References: 
  1. Boon NA, Colledge NR and Walker BR. Davidson's Principles and Practice of Medicine. Churchill Livingstone Elsevier, 2006; 20th edition.
  2. Management of cocaineA narcotic drug extracted from coca leaves.-associated chest pain and myocardial infarctionDeath of an area of heart muscle due to poor blood supply.: a scientific statement from the American Heart Association Acute Cardiac Care Committee of the Council on Clinical Cardiology. McCord J, Jneid H, Hollander JE et al. Circulation 2008;117:1897-1907.
  3. Myocardial infarction with angiographically normal coronaryRelating to the arteries supplying the heart itself. arteries. Chandrasekaran B and Kurbaan AS. J R Soc Med 2002;95:398-400.
  4. Longmore M, Wilkinson I and Török E. Oxford Handbook of Clinical Medicine 2002; 5th edition.