CHF is not a disease in itself. It is a syndrome in which the heart is unable to pump an adequate supply of blood to meet the oxygen requirements of the body's tissues and organs. The weakening of the heart as a pump in heart failure results in slow blood flow out of the heart to the rest of the body. This causes back up of blood in those chambers in the heart that are weakened and the veins that return blood to the heart from the rest of the body. The pooling of blood in the veins leads to the congestion of surrounding tissues and organs and the development of congestive symptoms such as leg edema (or swelling), nausea and bloating due to bowel edema, and shortness of breath due to lung edema. The development of these CHF symptoms and others depends on the severity of the heart failure, the time it took to develop (suddenly or gradually), and quality of treatment.
CHF is a symptom of an underlying cardiovascular problem; the disease process is often identified as a result of the symptoms of CHF. The most common causes are:
- Coronary artery disease and myocardial infarction (heart attack).
- Cardiomyopathy (diseased heart muscle).
- Hypertension (high blood pressure).
- Heart valve abnormalities (particularly the aortic and mitral valves).
- Heart arrhythmia (abnormal heart rhythm).
- Congenital heart defects (those occurring at birth).
- Toxic substances (excessive alcohol and drug abuse; certain environmental toxins).
- Iatrogenic (caused by medical therapies such as radiation, chemotherapy or certain treatments for AIDS
- Thyroid dysfunction
- Viral or bacterial infection
- Vitamin deficiency
- Idiopathic (meaning cause is unknown)
Left-sided versus right-sided heart failure
CHF may occur in one or both sides of the heart. As one side of the heart begins to fail, the other side can continue to function normally. However, untreated one-sided CHF often leads to excessive strain and subsequent CHF on the other side. CHF usually begins with the left side of the heart and progresses backward until the right side, too, fails. The left side of the heart receives oxygen-rich blood from the lungs and pumps it to the rest of the body. When the left side of the heart begins to fail, blood flow backs up into the lungs. Forward blood flow to the rest of the body may be impeded as well. With right-sided failure, the heart is unable to effectively pump blood to the left side and blood flow backs up to other parts of the body, including the legs and feet, liver, and gastrointestinal tract. Some of the symptoms may overlap.