Your heart is simply a pump. The left side of the heart pumps blood through your body; the right side pumps blood through your lungs. The principle is easy to understand. Oxygen is picked up by the blood going through the lungs, and distributed to the tissues, where it is used to burn up glucose to give you energy. The waste product of that energy, carbon dioxide, is picked up by the veins and carried to the right side of the heart, where it is pumped to the lungs and exchanged for more oxygen.
These are the straight facts, but they can give us no possible idea of how the heart carries out its job. No mechanical pump could perform as efficiently as the heart. No engineer can yet make a pump that acts around seventy times a minute for more than seventy years, meanwhile maintaining and repairing itself, supplying its own fuel— and not once, in all that time, breaking down or stopping for a rest!
In fact, there is no other muscle in the body like the heart. See how long you can continue to use your hand muscles without stopping. Grip a soft rubber ball in your stronger hand and squeeze it and relax just a little faster than once a second. Keep going for as long as you can. If you can manage five minutes before you tire then this is a good score. A trained athlete might last thirty minutes or more. Think of doing it day and night, without rest or sleep, for seventy years!
Yet that is what the heart does, all through your life. Most people never give it a second thought, but those who become aware of their heart beating can become neurotic about it, and their lives can be ruined. The first man-made heart valves used to ping with every beat, and their owners could hear it plainly, especially when everything was quiet at night. It was, to say the least, disturbing.
Never giving the heart a thought, however, has its downside. Taking it completely for granted can mean letting it become unhealthy. The more you understand about your heart, the better you can take care of it, and the less frightened you will be if things start to go wrong.
The first thing to understand is that the heart is a muscle, the myocardium (myo = muscle, cardia = heart). It differs from all other muscles in the body in its astonishing ability to recover extremely quickly from its previous contraction, or beat. It completes its cycle of shortening and lengthening within a fifth of a second, then has three- or four-fifths of a second to recover, to enable it to contract again..
In that vital resting time, the heart muscle reorganizes itself so that it can shorten again without tiring. In beating, it uses oxygen taken from the blood to convert the glucose within its stores into the energy needed for the contraction. In the rest between beats, each muscle fiber must take up more oxygen and glucose from the blood to replace the amounts lost in the previous contraction, and prepare it for the next contraction.
This constant flow of oxygen and glucose from bloodstream to myocardium is essential to life. Without them, the heart complains—and it usually does that via pain. And if the supply of oxygen and glucose to that particular part of the myocardium is not quickly restored, then that part of the muscle will die. The pain is called angina, but the death of the muscle is called infarction—or, in plain language, a heart attack. Keep the supply of oxygen and glucose enough to fulfill the demands of the heart, and it will keep going for the intended seventy-plus years.
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