Atherosclerosis is a progressive disease of the vasculature that is a common underlying pathology in stroke and heart attack. It is characterized by chronic inflammation, oxidative stress, and lipid accumulation within the vessel wall. Fatty streaks in atherosclerotic lesions contain foam cells, a cell type that develops from macrophages following their engulfment of large amounts of oxidized LDL. Hyper-proliferative and aberrant smooth muscle cells deposit proteoglycans around the plaque and contribute to vessel wall calcification and arterial stiffness. Proteolytic thinning of the fibrous cap promotes plaque rupture, followed by thrombus formation and complete blood flow blockage. Dysfunction of the smooth muscle layer can also lead to aneurysm formation with risk of extravascular bleeding. Risk factors for the development of atherosclerosis include high fat diet, smoking, advanced age, hypertension, and genetic mutations in key molecules.