Function of the Heart

Function of the Heart

Function of the Heart Although the heart’s right and left sides are separated from each other, they work together. Blood is squeezed through the chambers by a heart muscle contraction that begins in the thin-walled upper chambers, the atria, and is followed by a contraction of the thick muscle of the lower chambers, the ventricles. This active phase is called systole, and in each case, it is followed by a resting period known as diastole. One complete sequence of heart contraction and relaxation is called the cardiac cycle (Fig. 10-10). Each cardiac cycle represents a single heartbeat. At rest, one cycle takes an average of 0.8 seconds. The contraction phase of the cardiac cycle begins with contraction of both atria, which forces blood through the AV valves into the ventricles. The atrial walls are thin, and their contractions are not very powerful. However, they do improve the heart’s efficiency by forcing blood into the ventricles before these lower chambers contract. Atrial...
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