Recent cross-sectional, population-based echocardiographic studies show that about half of all patients with heart failure have preserved left ventricular systolic function (HF-PSF). Cohort studies of hospitalized patients show a smaller proportion of HF-PSF. Compared to those with reduced systolic function, patients with HF-PSF are more often female, older, less likely to have coronary artery disease, and more likely to have hypertension. Patients with HF-PSF are less symptomatic and receive different pharmacologic therapy than patients with reduced systolic function. Morbidity and mortality rates in patients with HF-PSF are high but not quite as high as in patients with reduced systolic function. Though much has recently been learned about the syndrome of HF-PSF, many questions remain to be answered, not least how it should be treated.