['To examine whether endogenous aldosterone can cause either arrhythmias (and some of their underlying mechanisms) or endothelial dysfunction in patients with coronary artery disease (CAD) but without heart failure.', 'Aldosterone blockade has been shown to reduce the incidence of sudden death in patients with heart failure. This could be caused by a reduction in arrhythmias or in coronary events. Whether either effect also occurs in other cardiac patients without heart failure is currently unknown.', 'We performed a randomized, placebo-controlled, double-blind crossover study on 98 patients with CAD but without heart failure on standard therapy, comparing 12.5-50 mg/day spironolactone (3 months) with placebo. Endothelial function was assessed by bilateral forearm venous occlusion plethysmography. Ventricular extrasystoles, procollagen III N-terminal peptide (PIIINP) and QT interval length were used to represent arrhythmias and their determinants.', 'Spironolactone produced a highly significant 75% reduction in ventricular extrasystoles (median 192, range 48-744) on placebo compared with spironolactone (median 48, range 19.2-288, P < 0.003). Spironolactone also decreased the QT interval from a mean of 440 +/- 28 to a mean of 425 +/- 25 (P < 0.001) and a collagen marker (PIIINP) from a mean of 3.6 +/- 0.9 to a mean of 3.0 +/- 0.8 (P < 0.001), but did not significantly change endothelial dysfunction or heart rate variability.'] Does spironolactone have antiarrhythmic activity in ischaemic cardiac patients without cardiac failure?