Light micrograph of tissue from a human heart 4 days after 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 pale pink, but the cells' nuclei are no longer visible. The white blood cells (leukocytes, dark dots) have infiltrated the area to begin clearing away the necrotic tissue by phagocytosis (engulfing and digesting). Image 3 in sequence of 3.