The present study explores the possibility of local de novo aldosterone production in normal and failing hearts (human and mouse) and the regulation of such putative cardiac steroidogenesis. Total RNA was isolated from human tissue from failing hearts taken at the time of cardiac transplantation, from normal hearts obtained at autopsy, and from normal and pressure-overloaded mouse hearts. Vascular smooth muscle cells from human artery and vein were also analyzed. RNA was reverse transcribed and probed with specific primers for side-chain cleavage enzyme (CYP11A), 3β-hydroxysteroid dehydrogenase, aldosterone synthase (CYP11B2), 11β-hydroxylase (CYP11B1), steroidogenic factor-1, and steroid acute regulatory protein. CYP11A, 3β-hydroxysteroid dehydrogenase-2, and steroid acute regulatory protein were expressed at modest levels in all tissues examined in both mouse and human. In failing human heart, CYP11B1 and CYP11B2 were detected in some samples, in contrast with normal hearts, which expressed neither; in the mouse heart steroidogenic factor-1 was detected, but neither CYP11B1 nor CYP11B2 was found. Steroidogenic factor-1 was detected in no human heart sample tested after 40 cycles of PCR. Although the expression of some steroidogenic genes can be detected in the heart, the likelihood of physiologically relevant levels of aldosterone production by the normal heart is very low. The exact cellular location of steroid synthesis in the failing human heart remains to be established.