The PRESERVE (Prospective Randomized Enalapril Study Evaluating Regression of Ventricular Enlargement) study is designed to provide a definitive test of the ability of enalapril to achieve greater left ventricular (LV) mass reduction than nifedipine GITs (gastrointestinal treatment system) by a degree that would be prognostically meaningful on a population basis (10 g/m2). To achieve this goal, an ethnically diverse population of 480 men and women with essential hypertension and increased LV mass of screening echocardiography will be enrolled at clinical centers on 4 continents and studied by echocardiography at baseline and after 6 and 12 months' randomized therapy. Blinded readings of echocardiograms at a central laboratory will provide systematic information about treatment effects on LV structure, wall motion, and Doppler blood flow. The study power is at least 90% to test the primary hypotheses that enalapril will induce greater normalization of LV mass and diastolic filling than nifedipine. After the 1-year echocardiographic trial, the study population will be followed 3 more years to test the hypothesis that a reduction in LV mass, independent of blood pressure lowering, is associated with a reduction in the risk of morbid and fatal cardiovascular events.