Heart attack. Light micrograph of a section through a human heart, following a heart attack (myocardial infarction). This occurs predominately due to a blood clot (thrombus) blocking a coronary artery, which can be caused by a high-fat, low- fibre diet. Necrotic (dead) muscle fibres stain deeper red and do not show a nuclei, compared to living muscle. Between the living and dead muscle there is vascular tissue. If the patient survived the heart attack, the dead muscle would have been digested and a fibrous scar formed. Magnification unknown.