The study is to demonstrate non-inferiority of spironolactone vs. eplerenone in preserving cardiac and pulmonary function in patients with preserved LV ejection fraction. Males with Duchenne muscular dystrophy (DMD) confirmed clinically and by mutation analysis will be enrolled. Subjects will be randomized to either eplerenone or spironolactone. Subjects will use a drug diary to record daily compliance of taking the study medication as well as any concerns they may have during the study period. Subjects will undergo cardiac magnetic resonance imaging (CMR) and pulmonary function tests (PFT) at baseline and then again at 12 months post enrollment. Subjects will also complete a quality of life questionnaire at baseline and 12 months. Degree of elbow contracture will be measured using a goniometer at baseline and 12 months.