This study sought to examine the association of a borderline left ventricular ejection fraction (LVEF) of 50% to 55% with cardiovascular morbidity and mortality in a community-based cohort.Guidelines stipulate a LVEF >55% as normal, but the optimal threshold, if any, remains uncertain. The prognosis of a "borderline" LVEF, 50% to 55%, is unknown.This study evaluated Framingham Heart Study participants who underwent echocardiography between 1979 and 2008 (n = 10,270 person-observations, mean age 60 years, 57% women). Using pooled data with up to 12 years of follow-up and multivariable Cox regression, we evaluated the associations of borderline LVEF and continuous LVEF with the risk of developing a composite outcome (heart failure [HF] or death; primary outcome) and incident HF (secondary outcome).During follow-up (median 7.9 years), HF developed in 355 participants, and 1,070 died. Among participants with an LVEF of 50% to 55% (prevalence 3.5%), rates of the composite outcome and HF were 0.24 and 0.13 per 10 years of follow-up, respectively, versus 0.16 and 0.05 in participants having a normal LVEF. In multivariable-adjusted analyses, LVEF of 50% to 55% was associated with increased risk of the composite outcome (hazard ratio [HR]: 1.37; 95% confidence interval [CI]: 1.05 to 1.80) and HF (HR: 2.15; 95% CI: 1.41 to 3.28). There was a linear inverse relationship of continuous LVEF with the composite outcome (HR per 5 LVEF% decrement: 1.12; 95% CI: 1.07 to 1.16) and HF (HR per 5 LVEF% decrement: 1.23; 95% CI: 1.15 to 1.32).Persons with an LVEF of 50% to 55% in the community have greater risk for morbidity and mortality relative to persons with an LVEF >55%. Additional studies are warranted to elucidate the optimal management of these individuals.