Traditionally, the role of aldosterone in heart failure was thought to be a result of its effects on epithelial cells where it induces sodium reabsorption and potassium excretion with subsequent haemodynamic effects from intravascular volume expansion. On this basis, spironolactone, a non-selective aldosterone antagonist, has been used for the treatment of congestive heart failure to block aldosterone-mediated effects in epithelial cells. The Randomized Aldactone Evaluation Study (RALES), in which spironolactone was added to existing therapy in patients with heart failure, showed a significant reduction in morbidity and mortality. These results suggest that the role of aldosterone in the pathophysiology of cardiovascular disease may be more complex than previously recognised. There now is extensive experimental and growing clinical evidence for an important physiological role for aldosterone in the pathology of cardiac and renal disease. Classical effects of aldosterone are mediated via its nuclear receptor. Novel non-epithelial effects of aldosterone are mediated via a second messenger system, which involves activation of the sodium/hydrogen antiporter. These effects of aldosterone have been demonstrated in the kidney, vascular smooth muscle cell and leukocytes, and in the regulation of rapid corticotropin suppression. It has been hypothesised that cardiac damage induced by aldosterone is independent of the presence of hypertension. In support of this, experimental evidence demonstrates that cardiovascular damage induced by aldosterone can be prevented by administration of a selective mineralocorticoid receptor antagonist. These findings suggest the dissociation between cardiovascular lesions and high blood pressure, and highlight the importance of aldosterone in the pathological changes.