•           Coronary Heart Disease

A heart attack happens if the flow of oxygen-rich blood to a section of heart muscle suddenly becomes blocked and the heart can't get oxygen. Most heart attacks occur as a result of ischemic heart disease.

Ischemic heart disease is a condition in which a waxy substance called plaque builds up inside the coronary arteries. These arteries supply oxygen-rich blood to the heart. Fat, calcium, proteins, and inflammatory cells build up in the arteries to form plaques. These plaque deposits are hard on the outside and soft and mushy on the inside.

When the plaque is hard, the outer shell cracks. This is called a rupture. Platelets (disc-shaped things in your blood that help it clot) come to the area, and blood clots form around the plaque. If a blood clot blocks the artery, the heart muscle suffers from the lack of oxygen. The muscle cells soon die, causing permanent damage.

 When plaque builds up in the arteries, the condition is called atherosclerosis. The buildup of plaque occurs over many years.

Eventually, an area of plaque can rupture (break open) inside an artery. This causes a blood clot to form on the plaque's surface. If the clot becomes large enough, it can mostly or completely block blood flow through a coronary artery.

If the blockage isn't treated quickly, the portion of heart muscle fed by the artery begins to die. Healthy heart tissue is replaced with scar tissue. This heart damage may not be obvious, or it may cause severe or long-lasting problems.

•           Coronary Artery Spasm

A less common cause of heart attack is a severe spasm (tightening) of a coronary artery. The spasm cuts off blood flow through the artery. Spasms can occur in coronary arteries that aren't affected by atherosclerosis. During this coronary spasm, the arteries spasm on and off, cutting off the blood supply to the heart muscle (ischemia). It can happen while you’re at rest and even if you don’t have serious coronary artery disease.

Each coronary artery sends blood to a different part of your heart muscle. The severity of the muscle damage depends on the size of the area that the blocked artery supplies and the amount of time between the attack and treatment.

Your heart muscle starts to heal soon after a heart attack. This takes about 8 weeks. Just like a skin wound, a scar forms in the damaged area. But the new scar tissue doesn’t move the way normal tissue does. So your heart can’t pump as much after a heart attack. The extent of the ability to pump depends on the size and location of the scar.

The causes of a coronary artery spasm aren't always clear. A spasm may be related to:

•           Taking certain drugs, such as cocaine;

•           Emotional stress or pain;

•           Exposure to extreme cold;

•           Cigarette smoking.