Heart attacks occur when the blood supply to the heart muscle is suddenly interrupted or severely reduced. This interruption is most often caused by a blockage in one or more of the coronary arteries, usually due to a buildup of fatty deposits called plaques. When a plaque ruptures, a blood clot can form at the site, blocking the artery and stopping blood flow to part of the heart muscle. Without this blood supply, the heart muscle becomes damaged and may begin to die. This damage can be irreversible if not treated promptly. Other less common causes include severe spasms of a coronary artery that temporarily reduce or stop blood flow, or a sudden tearing of the coronary artery wall (spontaneous coronary artery dissection). Risk factors that increase the likelihood of heart attacks include smoking, high-fat diets, high cholesterol, high blood pressure, diabetes, obesity, lack of exercise, stress, and family history of heart disease. In summary, heart attacks occur when an artery delivering blood and oxygen to the heart is blocked, leading to damage or death of part of the heart muscle if blood flow is not restored quickly.