Effect of Isosorbide Mononitrate on Hypertension to Improve Left Ventricular Hypertrophy, Fibrosis and Myocardial Function

Inclusion Criteria: * Systolic blood pressure \>140 mmHg, diastolic blood pressure \> 90 mmHg. * An elevated left ventricular mass index (defined as \>60 g/m1.7 in women and 80 g/m1.7 in men) OR LV posterior wall thickness \>1.4 cm documented in a clinically indicated echocardiographic examination or magnetic resonance imaging scan within the previous 12 months. * Stable medical therapy as defined by: (1)No addition or removal of ACE inhibitors, angiotensin receptor blockers, beta-blockers, or calcium channel blockers for 30 days. (2)No change in dosage of ACE, angiotensin-receptor blocker, beta-blockers or calcium-channel blockers s of more than 100% for 30 days. * Current therapy with an ACE inhibitor, hydralazine or a statin, all of which have been shown to reduce nitrate tolerance. Exclusion Criteria: * Rhythm other than sinus rhythm (i.e., atrial fibrillation). * Non-cardiac condition limiting life expectancy to less than one year, per physician judgment. * Current or anticipated future need for nitrate therapy. * Valve disease (\> mild aortic or mitral stenosis; \> moderate aortic or mitral regurgitation). * Hypertrophic cardiomyopathy. * Known infiltrative or inflammatory myocardial disease (amyloid, sarcoid). * Pericardial disease. * Primary pulmonary arteriopathy. * Have experienced a myocardial infarction or unstable angina, or have undergone percutaneous transluminal coronary angiography (PTCA) or coronary artery bypass grafting (CABG) within 60 days prior to consent, or requires either PTCA or CABG at the time of consent. * Resting heart rate (HR) \> 100 bpm. * A reduced LV ejection fraction (EF\<50%). * Known severe liver disease (AST \> 3x normal, alkaline phosphatase or bilirubin \> 2x normal). * Patients with a clinically indicated stress test demonstrating significant ischemia within a year of enrollment which was not followed by percutaneous or surgical revascularization. * Allergy to isosorbide mononitrate. * Current therapy with phosphodiesterase inhibitors, such as sildenafil, vardenafil or tadalafil, since the combination of nitrates and phosphodiesterase inhibitors can result in severe hypotension. * Therapy with rosiglitazone, since this combination is not recommended based on epidemiologic data suggesting that it may increase the risk of myocardial ischemia. * Current pregnancy or a positive urine pregnancy test. Women who become pregnant during the study will be discontinued from the trial. * Contraindications to a cardiac MRI: (i) Central nervous system aneurysm clips; (ii) Implanted neural stimulators; (iii) Implanted cardiac pacemaker or defibrillator; (iv) Cochlear implant; (v) Ocular foreign body (e.g. metal shavings); (vi) Other implanted medical devices: (e.g. drug infusion ports); (vii) Insulin pump; (viii) Metal shrapnel or bullet; (ix) Claustrophobia; (x) Extreme obesity rendering the patient unable to fit into narrow-bore scanners; (xi) Unwillingness of the patient to undergo a cardiac MRI. All patients with metallic implants will be individually evaluated prior to MRI.