Seventy percent of all cases of congestive heart failure are due to poor blood supply to the heart. High blood pressure, also known as hypertension, is also a factor. High blood pressure causes the heart muscle to become stiff so it cannot accept all the blood returning from the body and lungs. This causes congestion. As well, there can be problems with the aortic valve and the mitral valves, which can lead to heart failure.

Damage to the heart muscle can also be caused by infections, alcohol, deposits of iron and proteins in the heart and toxins.

Problems with the electrical (rhythm) component of the heart may also cause congestion, because the heart no longer pumps in steady rhythm, which allows blood to build up in the heart and tissues.

Noticeable symptoms of the left side of the heart not functioning well or failing:

• tiredness or fatigue, loss of energy, due to the reduction of oxygenated blood to your body
• shortness of breath. This may become apparent when you exert yourself, or when you are at rest. Shortness of breath is caused by fluid building up in your lungs because the heart cannot pump enough blood to drain your lungs.
• shortness of breath when lying flat. After lying down to rest, the excess fluid in the tissues is mobilized and the heart cannot pump efficiently enough to keep it from pooling in your lungs.
• coughing or wheezing. This can also be the result of fluid build-up in your lungs.

Noticeable symptoms of the right side of the heart not functioning well or failing:

• swelling of feet and ankles (edema), which is the result of a build-up of fluid in the tissues, which in turn is caused by the heart's inability to pump efficiently
• sudden weight gain, which is also due to fluid in your system that builds up because the heart can't pump efficiently
• loss of appetite, nausea or bloating. This may occur because your liver is congested from excess blood that cannot be pumped efficiently