False-colour arteriograph (angiograph) of the human heart, showing evidence of multiple stenosis (narrowing) in the left coronary artery (top right of heart on image). Unaffected blood vessels appear as continuous pink ribbons; the stenosed artery has a small diameter with a consequently reduced blood flow (ischaemia). The obstruction is due to formation of fatty atheroma plaques on the arterial wall; the presence of a blood clot (thrombosis) in such an obstructed region would lead to the total blockage of the artery and subsequent death of the section of heart muscle it services - an event known as an acute myocardial infarction or heart attack.