Myocardial infarction (MI) activates the renin-angiotensin system in the heart and increases local production of aldosterone. This hormone may increase reactive fibrosis in the myocardium favoring heart failure development. To elucidate the potential contribution of aldosterone to cardiac remodeling following MI, we evaluated the expression of mineralocorticoid receptors (MCR) in the left ventricle (LV) and kidney of rats after MI and captopril treatment. MI was induced by ligation of the coronary artery in Wistar rats, which were separated into (1) sham-operated group, (2) MI group, (3) MI-captopril treated group (cap, 50 mg kg(-1) day(-1)). One month later angiotensin converting enzyme (ACE) activity was assayed in the plasma, LV and kidney. Cardiac and renal angiotensin II (Ang II) levels were determined by ELISA and MCR mRNA expression and protein were measured by Taqman RT-PCR and Western blot, respectively. Cardiac MCR mRNA and protein levels increased nearly by 80% after MI and Cap treatment normalized cardiac MCR protein and mRNA expression. Kidney MCR expression was not affected. ACE activity increased 34% in the plasma and 83% in the LV after MI. This increase was prevented by Cap. Ang II concentration increased 225% in the LV and 193% in kidney, which was partially attenuated by Cap. Our data demonstrate upregulation of MCR in the heart following MI what may facilitate the effects of aldosterone in the ventricular remodeling process. ACE inhibitors may reduce reactive fibrosis not only by decreasing Ang II production but also by attenuating the aldosterone-signaling pathway by decreasing the expression of MCR receptors.