Objective: To test if collagen markers are associated with aldosterone-induced diastolic dysfunction. Background: Although primary aldosteronism is associated with more prominent cardiac remodeling and diastolic dysfunction, the reversibility of diastolic function is unclear. In addition, there is no known biomarker associated with aldosterone-induced diastolic dysfunction. Methods: We enrolled 27 patients with aldosterone-producing adenoma (APA) preparing for adrenalectomy, and 27 patients with essential hypertension prospectively from October 2006 to March 2010 at a tertiary referral center. Plasma matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) were measured, and echocardiography including tissue Doppler images was performed in both groups and 1 year after receiving adrenalectomy in the APA group. Results: The baseline plasma TIMP-1 level (88.438.7 vs. 63.6 +/- 32.5ng/ml; P=0.014), left ventricular mass index (LVMI), and E/E' ratio (11.5 +/- 2.9 vs. 9.0 +/- 2.1; P