Heart tissue death. Light micrograph of a section through heart muscle tissue (myocardium) three days following a heart attack (myocardial infarction). An infarction is tissue death (necrosis) caused by blockage of the tissue's blood supply (ischaemia). Here, the necrotic muscle tissue (myocardium) is a deep pink, but the cells' nuclei are no longer visible. The white blood cells (leucocyres, dark dots) have infitrated the area to begin clearing away the necrotic tissue by phagocytosis (engulfing and digesting).