BACKGROUND: Heart failure with preserved ejection fraction (HFpEF), traditionally considered a disease of the elderly, may also affect younger patients. However, little is known about HFpEF in the young. METHODS: We prospectively enrolled 1203 patients with HFpEF (left ventricular ejection fraction ≥50%) from 11 Asian regions. We grouped HFpEF patients into very young (<55 years of age; n=157), young (55-64 years of age; n=284), older (65-74 years of age; n=355), and elderly (≥75 years of age; n=407) and compared clinical and echocardiographic characteristics, quality of life, and outcomes across age groups and between very young individuals with HFpEF and age- and sex-matched control subjects without heart failure. RESULTS: Thirty-seven percent of our HFpEF population was <65 years of age. Younger age was associated with male preponderance and a higher prevalence of obesity (body mass index ≥30 kg/m2; 36% in very young HFpEF versus 16% in elderly) together with less renal impairment, atrial fibrillation, and hypertension (all P<0.001). Left ventricular filling pressures and prevalence of left ventricular hypertrophy were similar in very young and elderly HFpEF. Quality of life was better and death and heart failure hospitalization at 1 year occurred less frequently ( P<0.001) in the very young (7%) compared with elderly (21%) HFpEF. Compared with control subjects, very young HFpEF had a 3-fold higher death rate and twice the prevalence of hypertrophy. CONCLUSIONS: Young and very young patients with HFpEF display similar adverse cardiac remodeling compared with their older counterparts and very poor outcomes compared with control subjects without heart failure. Obesity may be a major driver of HFpEF in a high proportion of HFpEF in the young and very young.