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A single copy of these materials may be reprinted for noncommercial personal use only. This content does not have an English version. This content does not have an Arabic version. See more conditions. Chambers and valves of the heart. A double-layered membrane called the pericardium surrounds your heart like a sac. The outer layer of the pericardium surrounds the roots of your heart's major blood vessels and is attached by ligaments to your spinal column, diaphragm, and other parts of your body.
The heart weighs between 7 and 15 ounces to grams and is a little larger than the size of your fist. In fact, each day, the average heart beats , times, pumping about 2, gallons 7, liters of blood.
The inner layer of the pericardium is attached to the heart muscle. A coating of fluid separates the two layers of membrane, letting the heart move as it beats. Your heart has 4 chambers. But in other ways the Founders were mistaken. Senators have been directly elected by voters since the Seventeenth Amendment passed in and are much more likely to lose reelection campaigns — so they must work harder to curry favor if they want to keep their positions.
Members of the House, by contrast, seldom lose their reelection bids unless they have been marked by scandal or their districts have changed. They are more insulated from the popular passions that America's Founders feared they would express. Previous How a Bill Becomes a Law.
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