What is a heart attack?

 
A heart attack occurs when the flow of oxygen-rich blood to a section of heart muscle is suddenly blocked. If blood flow is not restored quickly, the section of heart muscle begins to die.
Heart attacks are a cause of death among men and women in the United States. The good news is that excellent treatments are available for heart attacks. These treatments can save lives and prevent disabilities. 
Treatment of a heart attack is more effective when administered immediately after the symptoms. If you think you or someone else is having a heart attack, call 9-1-1 immediately.
Overview
Heart attacks are most often occur due to coronary heart disease (CHD), also called coronary artery disease. CHD is a condition where a waxy substance called plaque (plak) builds up inside the coronary arteries.These arteries supply oxygen-rich blood to the heart. 
When plaque builds up in arteries, the condition is called atherosclerosis (ATH-er-o-skler-O-sis). Plaque build-up occurs for many years.
Finally, a plate may rupture zone (open) within an artery. Causing a blood clot to form on the surface of the plate. If the clot is large enough, they can usually or completely block blood flow in a coronary artery.
If the blockage is not treated promptly, the portion of heart muscle supplied by that artery begins to die. Healthy heart tissue is replaced by scar tissue.This heart damage may not be obvious, or may cause serious or long term.Figure A shows a heart with the heart muscle death from a heart attack.Figure B is a section of a coronary artery and plaque build-up of a blood clot.
A less common cause of heart attack is a severe spasm (narrowing) of a coronary artery. The spasm stops blood flow in the artery. The spasms may occur in coronary arteries that are not affected by atherosclerosis.
Heart attacks may be associated with or cause serious health problems such as heart failure and life-threatening arrhythmias (Rith-AH-ah-me).
Heart failure is a condition in which the heart can not pump enough blood to meet the needs of the body. Arrhythmias are irregular heartbeats.Ventricular fibrillation is a potentially fatal arrhythmia can cause death if not treated immediately.