blockage of blood circulation to a localized area or organ of the body resulting in tissue death. Infarctions commonly occur in the spleen, kidney, lungs, brain, and heart. The acute emergency known as myocardial infarction, or heart attack, is usually caused by a blockage in one of the coronary arteries that supply blood to the heart muscle. The blockage typically occurs when a blood clot (see thrombosis) lodges in an area already narrowed by arteriosclerosis; other causes are vasospasms in the arterial walls or viral infection of the heart. Symptoms include a crushing pain in the chest radiated to either arm (more commonly the left arm), the jaw, and the neck, although in some cases there are no symptoms at all. The seriousness of the infarction is dependent upon the amount of heart muscle affected, how long the area is deprived of blood, and whether it affects the natural pacemaker of the heart, setting off arrhythmias such as ventricular fibrillation. Death of heart muscle tissue and heart failure may result (see congestive heart failure); damage to other vital organs, including the brain, may occur if the heart is unable to pump necessary oxygen and blood to them. Confirmation of myocardial infarction is made by electrocardiography and measurement of elevations of white blood cells and certain enzymes. Treatment of acute myocardial infarction may include first aid in the form of cardiopulmonary resuscitation (CPR), an emergency balloon angioplasty, or the administration of beta-blockers and thrombolytic drugs (clot-dissolving drugs), such as tissue plasminogen activator. The healing of an infarction occurs through replacement of the dead tissue by scar tissue.

See also coronary artery disease.

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