In heart failure, the kidneys are fooled into believing that the body is dehydrated. This occurs because the amount of blood pumped from the heart to the kidneys is reduced due to heart failure. The kidneys respond to this decreased blood flow by retaining salt and water and decreasing urine production. In addition, the kidneys produce hormones that make people with heart failure feel thirsty. The extra fluid that is retained by the kidneys will eventually put an additional strain on the weakened heart and lead to fluid collecting in the lungs, abdomen, ankles or hands.
Diuretics force the kidneys to make more urine and to remove excess water and salt from the body.
As a result, diuretics help control swelling and shortness of breath. In combination with an ACE inhibitor, a diuretic can help provide good control over the symptoms of heart failure. The common side effects of diuretics include lightheadedness and low electrolyte levels in the blood. Many people who take diuretics need to take additional potassium, which is an electrolyte in the blood. Potassium levels that are too high or too low can be dangerous.