False-colour scintigram (gamma camera scan) of the human heart recorded during systole, the period of the cardiac cycle when the heart contracts and pumps blood around the circulation. The reduced size of the left ventricle is indicated by the small, roughly circular red area at bottom right. The left ventricle, the heart's major pumping chamber, has just contracted, pumping blood into the aorta for distribution around the system. The pink & white colour-coded area represents the region of greatest blood flow. The gamma scan is a map of the distribution of radioactivity following the intravenous injection of red blood cells labelled with the radio-isotope technetium-99m.
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