Abstract-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 (99Ϯ11 versus 88Ϯ10 pg/mL, PϽ0.01, and 100Ϯ12 versus 88Ϯ10 pg/mL, PϽ0.01, 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. Key Words: aldosterone Ⅲ angiotensin-converting enzyme Ⅲ natriuretic peptides Ⅲ hypertension, essential Ⅲ blood pressure T he renin-angiotensin-aldosterone system plays an important role in the control of body fluid and blood pressure. 1-3 Aldosterone promotes the retention of sodium and the loss of potassium, activates the sympathetic nervous system and myocardial and vascular fibrosis, and causes baroreceptor dysfunction. [1][2][3][4] Traditionally, aldosterone has been thought to be produced solely by the adrenal cortex in response to angiotensin II, making it an important component of the circulating renin-angiotensin-aldosterone system. Recently, aldosterone has also been reported to be produced in extraadrenal tissues, including the heart and blood vessels in animals. [5][6][7][8] The coronary sinus drains blood from the heart as a whole, and the anterior interventricular vein (AIV), which lies in the anterior interventricular groove, drains blood from the anterior left ventricle. 9 The difference in the hormone levels between the AIV and the aortic root therefore reflects the level of the hormone from the left ventricle, and that between the coronary sinus and the aortic root reflects the hormone level from the whole heart. By using this method, we showed that the production of natriuretic peptides, A-type natriuretic peptide (ANP) and B-type natriuretic peptide (BNP), was activated in the left ventricle in proportion to the severity of left ventricular dysfunction in patients with heart failure. 10 -13 We also showed by this method that the production of aldosterone and ACE was activated in the left ventricle in patients with heart failure in proportion to the severity of left ventricular dysfunction. 14,15 It is not known, however, whether aldosterone is also produced in the heart in patients with hypertension and without left ventricular systolic dysfunction.The present study was designed to examine whether aldosterone...