Blood clot, light micrograph. Thrombus (blood clot, centre) occluding an artery. The fibrous clot, which is packed full of blood cells and platelets, is preventing oxygen-carrying blood from reaching parts of the body. As a result, the tissue surrounding the thrombus has become inflamed, and tiny blood vessels (small white areas) have began to form across the occlusion in an effort to reinstate blood flow (a process called 'recanalisation'). If the occlusion occurs in arteries supplying the heart or brain, it can cause a fatal infarction or stroke.