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Over time, cholesterol buildup can occur in these blood vessels in the form of plaque. This narrows the artery and can restrict the amount of blood that can flow through it. If the artery becomes too narrow, it cannot supply enough blood to the heart muscle when it becomes stressed. Just like arm muscles that begin to hurt if you lift too much, or legs that ache when you run too fast; the heart muscle will ache if it doesn’t get adequate blood supply. This ache is called angina.

If the plaque ruptures, a small blood clot can form within the blood vessel and acutely block the blood flow. When that part of the heart loses its blood supply completely, the muscle dies. This is called a heart attack, or an MI – a myocardial infarction (myo=muscle +cardial=heart; infarction=death due to lack of oxygen).

Mostly heart attacks happen due to coronary artery disease; it is the buildup of plaque on the inner walls of the coronary arteries. Hardened plaque can break open, and attracts blood clot to form at the surface. A heart attack occurs if the blood clot is large enough to block most or cut off all of the blood supply to the artery.

Due to blockage oxygen rich blood cannot reach some parts of the heart muscle fed by the artery. Inadequate oxygen supply damages the heart muscle. If the blockage is not cleared quickly, the damaged heart muscle starts to die.

Heart attack may also happen due to problems with the microscopic blood vessels of the heart called micro-vascular disease. It is more common in women than in men.

Less common cause of heart attack is a sudden contraction (spasm – tightening) of the coronary artery that block blood flow through the artery. This contraction can occur in coronary artery that have or does not have coronary heart disease. It is still unknown what causes this coronary artery contraction, but mostly it is related to:

1.Exposing to cold temperatures
2.Mental stress or pain
3.Cigarette smoking
4.When taking cocaine

A heart attack occurs when one or more of the arteries supplying your heart with oxygen-rich blood (coronary arteries) become blocked. Over time, a coronary artery can become narrowed from the buildup of cholesterol. This buildup — collectively known as plaques — in arteries throughout the body is called atherosclerosis.

During a heart attack, one of these plaques can rupture and a blood clot forms on the site of the rupture. If the clot is large enough, it can block the flow of blood through the artery. When your coronary arteries have narrowed due to atherosclerosis, the condition is known as coronary artery disease. Coronary artery disease is the major underlying cause of heart attacks.

An uncommon cause of a heart attack is a spasm of a coronary artery that shuts down blood flow to part of the heart muscle. Drugs, such as cocaine, can cause such a life-threatening spasm.

A heart attack is the end of a process that typically evolves over several hours. With each passing minute, more heart tissue is deprived of blood and deteriorates or dies. However, if blood flow can be restored in time, damage to the heart can be limited or prevented.