Atherosclerosis is a condition where plaque builds up in the arteries, causing them to harden and narrow over many years without symptoms. It is caused by cholesterol and other substances combining to form plaque. This plaque buildup can lead to heart disease, heart attacks, and strokes, and is a major cause of death worldwide. Diagnosis involves laboratory tests of cholesterol levels, including total cholesterol, HDL, LDL, and fasting blood sugar. Risk factors include diabetes, smoking, lack of exercise, obesity, and high cholesterol diet. Prevention focuses on reducing dietary cholesterol, exercising regularly, avoiding tobacco and alcohol, and potentially using aspirin.