There is no information on heart failure (HF) with preserved ejection fraction (HFpEF, EF >50%) in children. Through a retrospective review of 3,907 pediatric patients with cardiovascular disease, we examined the characteristics of pediatric HFpEF over a 10-year period. We identified 18 patients with HFpEF (0.5%). They were predominantly young children (1.1±0.9 years, no sex preponderance), who had undergone surgery for congenital heart disease. They also had concentric hypertrophy and diastolic dysfunction with elevated blood pressure. Notably, HFpEF patients had more pronounced elevation of serum aldosterone but less pronounced elevation of plasma brain natriuretic peptide (BNP) than 22 systolic HF patients (SHF, EF ≤50%) (aldosterone: 1,375±1,200 vs. 511±563pg/ml, P<0.05, and BNP: 101±141 vs. 749±818pg/ml, P<0.005). Consequently, the aldosterone/BNP ratio was significantly higher in HFpEF (38±63) than in SHF (1.7±1.9, P<0.05), and an aldosterone/BNP ratio of 10.3 or higher best predicted HFpEF (area under the curve=0.89). The HF mortality rate was significantly lower in the HFpEF than in the SHF cases, and HF symptoms showed amelioration in 61% of patients during the follow-up period of 4.2±2.6 years. HFpEF does exist in children. A common pathophysiology underlies childhood and adult HFpEF despite considerable epidemiological and etiological differences. Future controlled studies are warranted to assess the cause-effect relationship between unique hormonal profiles and HFpEF.