Sometimes the arteries that feed into the heart narrow gradually over time, as a result of a cumulative accumulation of an obstruction (made up of fatty material). The amount of blood that can flow through the artery, and reach the heart, is reduced. Because blood carries oxygen, the heart is not able to receive the amount of oxygen it needs. Chronic disease often leads to heart attack, when a blood clot forms at the site where the artery is narrowed.