What happens during congestive heart failure?

Johns Hopkins Medicine
Congestive heart failure (CHF) can result from either a reduced ability of the heart muscle to contract or from a mechanical problem that limits the ability of the heart's chambers to fill with blood. When weakened, the heart is unable to keep up with the demands placed upon it; blood returns to the heart faster than it can be pumped out so that it gets backed up or congested.

The heart attempts to compensate for the congestion, or backup, of blood in a number of ways. It beats faster and expands somewhat more than usual as it fills with blood, so that when it contracts, more blood is forced out to the body. In addition, the decreased volume of blood reaching the kidneys causes them to start a hormonal cascade, which causes them to retain sodium and water, resulting in swelling or edema. These efforts help meet the body's demands in the short term, but they ultimately have very harmful long-term effects. Faster beating allows less time for the heart to refill after contraction, so less blood ends up being circulated. The increased effort means the heart muscle needs more oxygen, and if this need isn't met, it can be fatal.

Congestive heart failure is progressive and should not be confused with a heart attack, which involves sudden tissue death of the heart muscle. Although heart failure may occur suddenly in some cases, gradual loss of function is more common. Fatigue, shortness of breath on exertion and increased frequency of nighttime urination develop and worsen over time.

Failure of the left side of the heart (left-sided failure) is most common. It leads to increased pressure in the pulmonary veins in the lungs, which forces fluid into the surrounding microscopic air sacs (alveoli) that transfer oxygen to the bloodstream. As the alveoli fill with fluid, they no longer work properly, which limits the amount of oxygen available to the body and produces the most characteristic symptoms of congestive heart failure: fatigue and shortness of breath. In right-sided failure, the increased pressure in the veins returning blood from the rest of the body combined with the compensatory retention of sodium and water leads to fluid accumulation and swelling in the abdomen, liver and legs. Often, both left-and right-sided heart failure occur together.
Joan Haizlip, MSN
Cardiology (Cardiovascular Disease)
There are a lot of things that happen in congestive heart failure (CHF).  The heart is a pump. If the pump fails or weakens, blood cannot be pumped out as well as before.  As a result many symptoms appear:
  • Fluid builds up in the lungs making it hard to breathe (dyspnea)
  • Difficulty breathing while laying flat (orthopnea),
  • Swelling (edema) in dependent parts of the body, like the feet or legs. 
  • Confusion
Dr. Mehmet Oz, MD
Cardiology (Cardiovascular Disease)
In congestive heart failure, the heart cannot pump enough blood to meet the body’s needs, so it beats faster and the heart muscle gets bigger, eventually causing the heart to wear out. In addition, your body retains water and salt; the extra fluid build-up is called congestion. This animation explains congestive heart failure in more detail.

Discovery Health

When the heart begins to fail, first the sympathetic nervous system is activated. This increases the heart rate and the force of heart contractions, and the body's veins are constricted. These factors work together in order to increase cardiac output. But this also constricts arteries, and that increases blood pressure. The heart works harder and uses more oxygen; this may cause further deterioration of the heart over time.

Blood flow to the kidneys is then decreased. This activates the renin-angiotensin-aldosterone system. The kidney releases an enzyme called renin when blood flow is decreased.. Renin converts angiotensinogen, which is an inactive plasma protein, into an active hormone called angiotensin II. This is a powerful constrictor of both arteries and veins which stimulates the adrenal gland to secrete the hormone aldosterone. However, Aldosterone causes the kidneys to retain water and salt and this increases blood volume. The increased blood volume does help to maintain cardiac output - it increases the filling of the heart. But the increased blood volume and the vasoconstriction also increase blood pressure. This becomes a vicious cycle - the increased pressure causes edema, which makes for an increased workload, and which may further weaken the heart.

At the same time, the body increases the secretion of ADH, a hormone in the pituitary gland (anti-diuretic hormone), which causes the kidney to retain more fluid. This may increase blood volume and help cardiac output, but it also increases blood pressure, and the weakened heart has to work even harder.

The heart muscle itself also experiences changes. The thickness of the muscle layer increases (hypertrophy), which enables the heart to contract with greater force and to maintain cardiac output. But this increases the need for oxygen, and eventually leads to further deterioration. Dilation occurs, which is the heart enlarging by stretching and thinning its walls. Initially output may be increased because of the increase of the amount of blood that the heart can hold, however the dilation eventually fails and the disease worsens.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.