False-colour scintigram (gamma camera scan) of a human heart showing ischaemia (reduced blood flow) following myocardial infarction, the death of a section of heart muscle following a coronary thrombosis (a blockage in a coronary artery - a heart attack). The image displays the distribution of radioactivity emitted by a previously-injected radionuclide, Thallium-201, according to the amount of light given off by a scintillator (a gamma camera) as it is struck by radiations of different intensities. The red areas on image correspond to healthy heart muscle adequately supplied with blood. The yellow gap between red areas (bottom left) represents an ischaemic area.