The benefits of aldosterone receptor antagonists (spironolactone and eplerenone) for patients with heart failure were shown in 2 recent randomized controlled trials. Some of the proposed mechanisms of action of aldosterone antagonists are (1) inhibition of myocardial and vascular remodeling, (2) blood pressure reduction, (3) decreased collagen deposition, (4) decreased myocardial stiffness, (5) prevention of hypokalemia and arrhythmia, (6) modulation of nitric oxide synthesis, and (7) immunomodulation. Like many hormone receptors, the aldosterone receptor can be either nuclear or membrane bound. Most of the activities of the aldosterone receptor are subserved by the nuclear receptors and often lead to alterations in gene transcription. Although these agents are well tolerated in carefully selected patient populations that meet the inclusion criteria of large clinical trials, their use in unselected elderly patients with heart failure and multiple comorbidities has been associated with a significant risk of hyperkalemia and renal failure. Although no convincing data exist to predict which individual patients will respond to aldosterone inhibition, patients with more severe heart failure and those with acute myocardial infarction with concomitant heart failure or left ventricular dysfunction are most likely to respond. Theoretically, aldosterone receptor antagonists may also be beneficial in patients with more mild to moderate systolic heart failure or even in those with diastolic heart failure, although direct evidence is still lacking.