Arterial stiffness and cardiac function are important predictors of cardiovascular events in patients with hypertension, even with adequate blood pressure (BP) control. We evaluated whether a direct renin inhibitor, aliskiren, reduces arterial stiffness and modulates left ventricular function compared with a diuretic, hydrochlorothiazide, in elderly hypertensive patients. Twenty-one hypertensive patients [67 ± 14 (SD) yr] were randomly assigned to receive 6-mo aliskiren ( n = 11) or hydrochlorothiazide ( n = 10)-based therapy. We assessed β-stiffness of the local arteries, arterial elastance ( Ea), and echocardiographic variables, including early ( E) and late ( A) mitral inflow velocity, deceleration time of E, early ( E′) and late ( A′) diastolic mitral annular velocity, and left ventricular end-systolic elastance ( Ees) before and after treatment. BP decreased similarly ( P < 0.001) after both therapies. β-Stiffness of the carotid artery decreased after aliskiren but increased after hydrochlorothiazide treatment (aliskiren: 6.42 ± 2.34 pre vs. 5.07 ± 1.29 post; hydrochlorothiazide: 5.05 ± 1.78 vs. 7.25 ± 2.68, P = 0.001 for interaction). β-Stiffness of the femoral and radial arteries were not different after either treatment. Different from aliskiren, E decreased (73 ± 16 vs. 67 ± 14 cm/s, P = 0.026), and the deceleration time was prolonged (218 ± 40 vs. 236 ± 35 ms, P = 0.032) after hydrochlorothiazide therapy, whereas the E/ A, and E′ remained unchanged after both treatments. Ea and Ees decreased after aliskiren therapy (both P < 0.05), whereas the Ea/ Ees (ventricular-arterial coupling) was maintained after both treatments. Thus, aliskiren decreased the stiffness of carotid artery and left ventricular end-systolic elastance with maintenance of ventricular-arterial coupling without any effects on diastolic filling, while hydrochlorothiazide increased carotid arterial stiffness and slowed early diastolic filling in elderly hypertensive patients.