Classically, aldosterone is a steroid hormone secreted from the adrenal cortex, which acts on kidney, colon and sweat/salivary glands to promote unidirectional sodium transport. Currently, there is excellent experimental evidence for aldosterone acting directly on the central nervous system to raise blood pressure, and on the heart to cause cardiac hypertrophy and fibrosis. In addition, there is emerging evidence for aldosterone synthesis in the heart, and for as yet unexplained benefits of aldosterone antagonism in the treatment of cardiac failure.