Renin, angiotensin II and aldosterone levels are elevated in congestive heart failure, especially when diuretics are introduced. This activation is clearly deleterious by elevating myocardial workload and is related to prognosis of heart failure. The link between hormonal activation and prognosis is causal, as hormonal inhibition by converting enzyme inhibitors improves heart failure prognosis. Angiotensin II and aldosterone appears to be toxic for the myocardium. The results of the trial conducted with angiotensin II antagonist losartan confirm data derived from converting-enzyme-inhibitors trials. The exact role of aldosterone is currently being evaluated in the RALES programme.