MEDIMAGE / SCIENCE PHOTO LIBRARY MEDIMAGE / SCIENCE PHOTO LIBRARY
Heart. Gross specimen of a heart that has been sliced in two, vertically. The heart is a muscular pump consisting of four chambers; two upper chambers, the atria, and two lower chambers, the ventricles. Here the thick muscular U-shaped walls of the ventricles can be clearly seen. The deep folds within the walls are the papillary muscles, which are attached to the heart valves by chordae tendineae (threads). The muscles maintain the integrity of the valves, which prevent the backflow of blood within the heart.
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