Micrograph showing a transverse section of a coronary artery with coronary atherosclerosis and thrombosis. Atherosclerosis is the thickening and hardening of the arterial wall due to a buildup of plaque in the artery. As the artery walls thicken, blood flow is reduced and the arteries may eventually become blocked. Thrombosis is the formation of a blood clot (thrombus) in a blood vessel. The clot can reduce blood flow and result in anoxia (oxygen deprivation) and infarction (cell death).