Heart failure means that your heart muscle doesn't pump as much blood as your body needs. Because your heart cannot pump well, your heart and your body try to make up for it. This is called compensation.
Your body has a remarkable ability to compensate for heart failure. The body may do such a good job that many people don't feel symptoms in the earlier stages of heart failure. It is only when your body isn't able to compensate enough that you will begin to experience symptoms.
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Compensation may help your body adjust to the effects of heart failure in the short term. But over time it can make heart failure worse by further enlarging the heart and reducing the pumping ability of the heart.
How does the body compensate?
With heart failure, the heart doesn't pump as well as it should. So your body doesn't get enough blood and oxygen. When this occurs, the body believes that there isn't enough fluid inside its vessels. The body's hormone and nervous systems try to make up for this by increasing blood pressure, holding on to salt (sodium) and water in the body, and increasing heart rate. These responses are the body's attempt to compensate for the poor blood circulation and backup of blood.
The nervous system. If your body senses that the brain and vital organs aren't receiving enough blood, the sympathetic nervous system starts working to get more blood to your brain and organs. This system releases substances called catecholamines into the bloodstream. These substances cause the blood vessels to constrict and speed up the heart rate. At the same time, the arteries supplying the brain and vital organs widen to carry the increased blood flow.
Hormone systems. When the body thinks it needs more fluid in its blood vessels, it releases specific chemicals (renin, angiotensin, and aldosterone) that cause the blood vessels to constrict. In addition, these hormones cause the body to retain more sodium and water. This adds fluid to your circulatory system. This fluid becomes part of the blood circulating throughout your system.