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Work of the Human Heart.

The human heart contracts from the first moment of life until the last one. The contractions of the heart pump the blood through the arteries to all the parts of the body. Scientists have determined that the total weight of the blood pumped by the heart daily is about ten tons.

The rate of heart contractions is regulated by two groups of nerve fibers. It varies in different persons and at different age.

Physiologists have determined that in the adult the heart makes from 60 to 72 beats per minute. In children the rate of heartbeat is much higher. Research work of many scientists has helped to determine that the rate of heartbeat increases depending on different emotions.

Each beat of the heart is followed by a period of rest for the cardiac muscle. Each wave of contraction and a period of rest following it compose a cardiac cycle.

Research work has given physiologists the possibility to find out that the heart muscle works or contracts about one third of the time of the person's life. The period of rest is shorter during greater physical exertion and longer when the body is at rest.

Each cardiac cycle consists of three phases: physiologists have called the first phase of short contraction of both atria - the atrial systole. They have called the second phase of a more prolonged contraction of both ventricles - the ventricular systole. The period of rest of the cardiac muscle is called the diastole.

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