Description: Hypertension (HTN) is a major risk factor for heart failure. We investigated the influence of HTN on cardiac contraction and relaxation in transgenic renin overexpressing rats (carrying mouse Ren-2 renin gene, mRen2, n = 6). Blood pressure (BP) was measured. Cardiac contractility was characterized by echocardiography, cellular force measurements, and biochemical assays were applied to reveal molecular mechanisms. Sprague-Dawley (SD) rats ( n = 6) were used as controls. Transgenic rats had higher circulating renin activity and lower cardiac angiotensin-converting enzyme two levels. Systolic BP was elevated in mRen2 rats (235.11 ± 5.32 vs. 127.03 ± 7.56 mmHg in SD, P 〈 0.05), resulting in increased left ventricular (LV) weight/body weight ratio (4.05 ± 0.09 vs. 2.77 ± 0.08 mg/g in SD, P 〈 0.05). Transgenic renin expression had no effect on the systolic parameters, such as LV ejection fraction, cardiomyocyte Ca 2+ -activated force, and Ca 2+ sensitivity of force production. In contrast, diastolic dysfunction was observed in mRen2 compared with SD rats: early and late LV diastolic filling ratio (E/A) was lower (1.14 ± 0.04 vs. 1.87 ± 0.08, P 〈 0.05), LV isovolumetric relaxation time was longer (43.85 ± 0.89 vs. 28.55 ± 1.33 ms, P 〈 0.05), cardiomyocyte passive tension was higher (1.74 ± 0.06 vs. 1.28 ± 0.18 kN/m 2 , P 〈 0.05), and lung weight/body weight ratio was increased (6.47 ± 0.24 vs. 5.78 ± 0.19 mg/g, P 〈 0.05), as was left atrial weight/body weight ratio (0.21 ± 0.03 vs. 0.14 ± 0.03 mg/g, P 〈 0.05). Hyperphosphorylation of titin at Ser-12742 within the PEVK domain and a twofold overexpression of protein kinase C-α in mRen2 rats were detected. Our data suggest a link between the activation of renin-angiotensin-aldosterone system and increased titin-based stiffness through phosphorylation of titin's PEVK element, contributing to diastolic dysfunction. Listen to this article's corresponding podcast at http://ajpheart.podbean.com/e/diastolic-dysfunction-in-the-hypertensive-mren2-rat/ .