Animal studies suggest that aldosterone produces vascular inflammation, endothelial dysfunction and tissue injury/firosis. We have studied the effect of aldosterone blockade in 2 populations of heart failure and 1 population of diabetes mellitus. In both heart failure populations, spironolactone improved endothelial function and reduced vascular ACE activity. By contrast, spironolactone significantly worsened endothelial function in Type 2 diabetics. The latter effect may be because spironolactone increased HbAlc and plasma angiotensin II. Overall, therefore, aldosterone blockade improves vascular function in heart failure but further work in other populations are required to assess the potential of aldosterone blockade in non heart failure vascular patients.