Aldosterone is a steroid hormone produced by the renal cortex (the outer portion of the kidney). It directly regulates blood pressure by expanding extracellular fluid volume. Aldosterone antagonists prevent this, help eliminate extra fluid from the body, offload the heart and reduce leg oedema (swelling).

Spironolactone and eplerenone are examples of aldosterone antagonists. These drugs are helpful in combination with beta-blockers, ACE inhibitors (ACE-I) or angiotensin receptor blockers (ARBs), and diuretics for patients with heart failure as they improve symptoms and survival. Aldosterone antagonists are beneficial in people with scarring of the heart muscle after a heart attack to prevent cardiac remodelling, i.e. enlargement of the heart and deterioration of the pumping function. Especially spironolactone is also a very effective treatment for resistant hypertension.

Like other drugs, aldosterone antagonists may have some side effects. Spironolactone and eplerenone may interfere with kidney function and lead to an increased potassium level in the blood. Patients on aldosterone antagonists should therefore have regular blood tests to check kidney function and potassium level. Spironolactone may lead to gynecomastia, a painful swelling of breasts; eplerenone does not have this side effect.