Exercise intolerance due to HFPEF is a major cause of disability among older Americans. Several lines of evidence suggest that aldosterone antagonism may improve exercise tolerance in HFPEF. Therefore, the primary aim of this study is to test the hypothesis that spironolactone will improve exercise tolerance and quality of life in elderly patients with isolated HFPEF. A total of 72 participants aged 60 or older will be randomized to receive either spironolactone 25mg daily or a placebo.