Why is the heart able to work at such a high rate? First of all, it is not absolutely correct to think that the heart works without rest. The cardiac muscle quite often rests, but the periods of rest are very brief. A heart beat lasts for about-0.49 of a second and, if a man is resting, a 0.31 second interval follows each beat. The period of rest is actually longer since not all parts of the heart work simultaneously.

The heart cycle starts with the contraction of the auricles, whilst the ventricles rest, and the ventricles contract while the auricles relax. The auricles take about 0.11-0.14 of a second to contract and this is followed by a 0.66 second rest. In other words, every day they work for no more than 3.5-4 hours and rest for about 20 hours. The ventricles take somewhat longer to contract, about 0.27-0.35 second, and rest for 0.45-0.53 second. Consequently, every twenty-four hours the heart’s ventricles work for 8.5-10.5 hours and rest for 13.5-15.5 hours.

In little birds the heart also rests, but their hearts contract and rest more frequently. The heart of a willow tit contracts 1000 times per minute; a single contraction of the auricles lasts 0.014 second with an ensuing rest of 0.046 second. The ventricles contract for 0.024 and rest for 0.036 second. Thus, the auricles work for only 5 hours 40 minutes and rest for 18 hours 20 minutes, whilst the ventricles work for 9 hours 36 minutes and rest for 14 hours 24 minutes. This differs very little from man’s.

Nevertheless, man is quite able to considerably improve the way in which his heart works by prolonging the period of its rest. According to medical research, in a well-trained sportsman the heart, when at rest, contracts less frequently than the heart of other people, the frequency being as low as 40 and even 28 beats per minute.

To cope with such a tremendous task as is the lot of the heart, rest alone is not enough. The heart must also be well nourished and have a good supply of oxygen. This explains why the heart in higher animals has its own, very powerful circulation system.

April 21, 2010 at 12:02 pm by admin
Category: Action of Heart
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