Atherosclerosis is the gradual buildup of plaque in the walls of your arteries. Arteries are blood vessels that carry oxygen-rich blood to organs and tissues throughout your body. Plaque (atheroma) is a sticky substance made of fat, cholesterol, calcium and other substances.

As plaque builds up, your artery wall grows thicker and harder. This “hardening of the arteries” is usually a silent process in the early stages. You may not notice symptoms for a long time. But eventually, as the plaque grows, the opening (lumen) of your artery narrows, leaving less room for blood to flow. This means less blood can reach your organs and tissues. Plus, the constant force of blood flow can lead to plaque erosion or rupture, causing a blood clot to form.

A narrowed artery is like a highway reduced to one lane. But a blood clot is like a barricade in the middle of the road. It blocks blood flow to certain organs or tissues the artery normally feeds. The effects on your body depend on where the blood clot forms. For example, blockages in a coronary artery deprive your heart of oxygen-rich blood, leading to a heart attack.