The purpose of this study is to determine whether LCZ696 (valsartan/sacubitril) is safe and has beneficial effects on the heart and blood vessels in patients with high blood pressure and/or diabetes or other risk factors for developing heart failure (elevated levels of natriuretic peptide and elevated left atrial volume index). Patients will be randomized to receive LCZ696 or valsartan (and matching placebo) for 18 months to assess the impact on left ventricular diastolic function.