The purpose of this project is to determine if eplerenone, an aldosterone blocker, prevents remodelling of the heart in patients with controlled essential hypertension, defined as having a blood pressure of equal to or less than 130/80 in diabetics and equal to or less than 140/90 in non-diabetics. This study will investigate if the addition of 25 milligrams of eplerenone daily to a subject's hypertension medication regimen will prevent the progression or development of diastolic dysfunction. Echocardiography will be used to measure the changes in heart structure of subjects receiving eplerenone versus subjects receiving placebo (a drug that may resemble the study drug but contains no active ingredient). Approximately 30 subjects will take part in this study.