A heart attack is caused by the formation of a blood clot in a coronary artery. When the body's cholesterol levels are too high, it causes deposits of fatty substances known as plaque to build up along the interior walls of the blood vessels. These deposits also contain white blood cells, which build up inside the lining of the blood vessels instead of circulating around the body. Over time, these fatty deposits will rupture or split, and the blood vessel will try to repair itself by forming a blood clot, which then further constricts the surrounding blood vessels. If a rupture occurs in a small blood vessel, the patient may only experience chest pain. However, if the blood clot forms in a large blood vessel such as a coronary artery, it can result in death.