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 obstruction of a coronary artery - a heart attack. The image shows the uptake of a radio-isotope, Thallium-201, by the heart's muscle cells. Radioactive emissions recorded by the gamma camera are colour-coded to reveal a defect (\cold spot\"), represented by the smaller red area at left - the red & white areas represent normal heart muscle. This form of \"cold- spot\" scanning is used to demonstrate ischaemia by comparing scans taken at rest & during exercise."