In spite of treatment with inhibitors of the renin-angiotensin system, plasma levels of aldosterone increase progressively in heart failure. This phenomenon of aldosterone escape is associated with adverse outcome. The aldosterone receptor antagonists spironolactone and eplerenone can improve prognosis for patients with heart failure. The commonest, and often problematic unwanted effect of these agents, hyperkalaemia, may limit their usefulness and brings with it the need for careful clinical and biochemical monitoring. Recent trials, however, have shown clear benefits for large groups of patients for spironolactone (in severe chronic heart failure) and eplerenone (heart failure soon after acute myocardial infarction). Due consideration should be given to the addition of the appropriate aldosterone antagonist in suitable patients.