A heart attack, medically known as a myocardial infarction, occurs when the blood supply to part of the heart muscle becomes blocked, most often due to the buildup of plaque (a mixture of fat, cholesterol, and other substances) in the coronary arteries. When a plaque ruptures, a blood clot can form, completely blocking blood flow and depriving the heart muscle of oxygen. If not quickly restored, this causes permanent damage to heart tissue. A heart attack can occur suddenly and at any time, often triggered by physical exertion, emotional stress, or plaque rupture. According to the American Heart Association (AHA) and World Health Organisation (WHO), it is a medical emergency, and symptoms such as chest pain or pressure, shortness of breath, sweating, nausea, or pain radiating to the arm, neck, jaw, or back require immediate medical attention.