Background: Heart Failure (HF) is a frequent cause of mortality and recurrent hospitalization. Although HF databases are assembled based on left ventricular (LV) ejection fraction, patients without LV ejection fraction determination are not further analyzed. Objective: The purpose of this study is to characterize patient attributes and outcomes in this group-HF with unknown Ejection Fraction (HFunEF). Methods: We queried the electronic medical record from a community-based university practice for patients with a HF diagnosis. We included patients with >60 days follow-up and had interpretable Doppler-echocardiograms. We recorded demographic, Doppler-echocardiographic, and outcome variables (up to 2083 days). Results: There were 820 patients: 269 with HF with preserved Ejection Fraction (HFpEF), 364 with HF with reduced Ejection Fraction (HFrEF), of which 231 had a LV ejection fraction=40-49% and 133 had a LV ejection fraction<40%, and 187 with HFunEF. As compared to patients with HFunEF, HFpEF patients were younger, had a higher coronary disease and hyperlipidemia prevalence. Patients with HFrEF had more prevalent coronary disease, myocardial infarction, and hyperlipidemia. Patients with HFunEF were more likely to be seen by non-cardiology providers. All-cause mortality (ACM) was greater in HFunEF patients than patients with HFpEF (Hazard Ratio (HR)=1.60 (1.16-2.29), p=0.004). Furthermore, HF readmission rates were lower in HFunEF as compared to HFpEF (HR=0.33 (0.27-0.54), p<0.0001) and HFrEF (HR=0.30 (0.028-0.50), p<0.0001). Conclusion: Patients with HFunEF have greater ACM and lower HF re-admission than other HF phenotypes. Adherence to core measures, including LV ejection fraction assessment, may improve outcomes in this cohort of patients.