A heart attack—also called myocardial infarction or MI—occurs when an area of heart muscle is completely deprived of blood, and the heart muscle cells die.

A heart attack may result when plaque inside the heart arteries breaks open or ruptures, forming a clot that significantly blocks blood flow through the artery.

A plaque is made up of cholesterol, white blood cells, calcium, and other components, and it is surrounded by a fibrous cap. This fibrous cap may tear or rupture if blood suddenly flows faster or if the artery suddenly narrows. A tear or rupture signals the body to repair the injured artery lining—much as it might heal a cut on the skin—by forming a blood clot to seal the area. A blood clot that forms in an artery can completely block blood flow to the heart muscle and cause a heart attack.

Symptoms of a heart attack include:

• Chest pain or pressure, or a strange feeling in the chest.
• Sweating.
• Shortness of breath.
• Nausea or vomiting.
• Pain, pressure, or a strange feeling in the back, neck, jaw, or upper belly, or in one or both shoulders or arms.
• Lightheadedness or sudden weakness.
• A fast or irregular heartbeat.

Call or other emergency services immediately if you think you are having a heart attack. Medicines and procedures like angioplasty get blood flowing back to the heart to prevent death.

Heart attack symptoms do not go away with rest or nitroglycerin.