Background-Hypertension is an important clinical problem and is often accompanied by left ventricular (LV) hypertrophy and dysfunction. Whether the myocardial high-energy phosphate (HEP) metabolism is altered in human hypertensive heart disease and whether this is associated with LV dysfunction is not known. Methods and Results-Eleven patients with hypertension and 13 age-matched healthy subjects were studied with magnetic resonance imaging at rest and with phosphorus-31 magnetic resonance spectroscopy at rest and during high-dose atropine-dobutamine stress. Hypertensive patients showed higher LV mass (98Ϯ28 g/m 2 ) than healthy control subjects (73Ϯ13 g/m 2 , PϽ0.01). LV filling was impaired in patients, reflected by a decreased peak rate of wall thinning (PRWThn), E/A ratio, early peak filling rate, and early deceleration peak (all PϽ0.05), whereas systolic function was still normal. The myocardial phosphocreatine (PCr)/ATP ratio determined in patients at rest (1.20Ϯ0.18) and during stress (0.95Ϯ0.25) was lower than corresponding values obtained from healthy control subjects at rest (1.39Ϯ0.17, PϽ0.05) and during stress (1.16Ϯ0.18, PϽ0.05). The PCr/ATP ratio correlated significantly with PRWThn (rϭϪ0.55, PϽ0.01), early deceleration peak (rϭϪ0.56, PϽ0.01), and with the rate-pressure product (rϭϪ0.53, PϽ0.001). Conclusions-Myocardial HEP metabolism is altered in patients with hypertensive heart disease. In addition, there is an association between impaired LV diastolic function and altered myocardial HEP metabolism in humans.