This study was designed to examine whether aldosterone is produced from the hearts of patients with essential hypertension without left ventricular systolic dysfunction (LVSD). The study population consisted of 20 patients with essential hypertension without LVSD and 22 control subjects. Plasma levels of aldosterone, serum ACE activity, and B-type natriuretic peptide levels were measured in the anterior interventricular vein (AIV), coronary sinus, and aortic root during cardiac catheterization. The plasma aldosterone levels were significantly higher in AIV and coronary sinus than in aortic root (99±11 versus 88±10 pg/mL,P<0.01, and 100±12 versus 88±10 pg/mL,P<0.01, respectively) in the hypertension group. On the other hand, there were no significant differences in aldosterone levels for these sites in the control group. There were no significant differences in ACE activity levels between aortic root, AIV, and coronary sinus in either the hypertension or control group. The levels of B-type natriuretic peptide were significantly higher in AIV than in aortic root in both groups. The difference in aldosterone levels between AIV and aortic root (&Dgr; Aldo[AIV−Ao]) had a significant positive correlation with the difference in ACE activity between AIV and aortic root (&Dgr;ACE[AIV−Ao]) (r=0.501,P<0.05) in the hypertension group. Both &Dgr; Aldo[AIV−Ao] and &Dgr;ACE[AIV−Ao] had a significant positive correlation with diastolic blood pressure (r=0.498,P<0.05;r=0.577,P<0.01, respectively) in the hypertension group. We conclude that production of aldosterone is activated in the left ventricles in patients with essential hypertension without LVSD in proportion to the severity of hypertension.