The most common type of heart failure in elder persons is heart failure with preserved ejection fraction (HFPEF) and more than 80% of people with such heart failure are overweight or obese.   Exercise intolerance is the most common symptom of chronic HFPEF and a significant predictor of poor quality of life (QOL). The objective was to determine if calorie restriction (diet) or aerobic exercise training (exercise) improves exercise capacity and quality of life in obese older HFPEF patients. From February 2009 to November 2014, randomized, attention-controlled, 2 × 2 factorial experiments were undertaken in an urban university medical center. 100 older obese people with chronic, stable HFPEF were enrolled out of 577 initially screened subjects (mean [SD]: age, 67 years [5]; BMI, 39.3 [5.6]). (366 excluded by inclusion and exclusion criteria, 31 for other reasons, and 80 declined participation). Diet, exercise, or both for 20 weeks; attention control was by phone calls every two weeks. Exercise capacity measured as peak oxygen consumption (VO2, mL/kg/min; co-primary outcome) and QOL measured by the Minnesota Living with Heart Failure (MLHF) Questionnaire (score range: 0–105, higher scores indicate worse heart failure–related QOL; co-primary outcome). Of the 100 people who signed up, 26 were assigned to exercise, 24 to diet, 25 to exercise Plus diet, and 25 to control. The experiment was completed by 92 of these people. Diet adherence was 99% (SD, 1%).and exercise attendance was 84% (SD, 14%).  Peak VO2  was significantly enhanced by both interventions in main effects analysis: exercise, 1.2 mL/kg body mass/min (95% Confidence interval, 0.7 to 1.7), P less than .001; diet, 1.3 mL/kg body mass/min (95% Confidence interval, 0.8 to 1.8), P less than .001. For peak VO2  (joint effect, 2.5 mL/kg/min), the combination of exercise and nutrition was additive (complementary). Exercise and nutrition had no statistically significant effects on the MLHF total score (primary effect: exercise, -1 unit [95% Confidence interval, 8 to 5], P=.70; diet, -6 units [95 % Confidence interval, -12 to 1], P=.08). Peak VO2  changed in tandem with percent lean body mass (r=0.32; P=.003) and thigh muscle: intermuscular fat ratio (r=0.27; P=.02). There were no significant adverse events associated with the trial. In the diet group, bodyweight reduced by 7% (7 kg [SD, 1]), 3% (4 kg [SD, 1]) in the exercise group, 10% (11 kg [SD, 1]) in the exercise + diet group, and 1% (1 kg [SD, 1]) in the control group. Caloric restriction or aerobic exercise training enhanced peak VO2  in obese older adults with clinically stable HFPEF, and the effects may be cumulative. Neither intervention had a substantial impact on the MLHF Questionnaire-measured quality of life.