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 hypertensives. Twenty one hypertensives [67±14 (SD) yrs] were randomly assigned to receive 6-month 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 similarly decreased (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 prolonged (218±40 vs. 236±35 ms, P=0.032) after hydrochlorothiazide therapy, while the E/A, and E' remained unchanged after both treatments. Ea and Ees decreased after aliskiren therapy (both P<0.05), while 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 hypertensives.