BACKGROUND: Heart failure has been called the "new epidemic of cardiovascular disease," but few studies have described key epidemiologic measures of the syndrome in geographically defined US populations. METHODS AND RESULTS: We obtained lists of discharge diagnosis codes in 1995 from 22 Minneapolis-St. Paul metropolitan area hospitals; identified patients 35 to 84 years old with a heart failure discharge code; and sampled and abstracted 50% of the hospital records. To identify heart failure-related hospitalizations, we applied 6 published definitions of the syndrome to the sample and selected cases that met at least 4 of the 6 definitions (n = 2887). The patient cohort was followed for 5 to 6 years to ascertain deaths. The rate of hospitalized heart failure ranged from a few dozen hospitalized patients per 100,000 residents ages 35 to 44 years to more than 2000 per 100,000 residents ages 75 to 84, and was consistently higher among men than among women (age-adjusted rate ratio 1.46; 95% CI 1.39-1.54). Within 1-year of the index admission, 37% of male patients and 30% of female patients have died-10 times the annual mortality of the source population. By the end of the follow-up, cumulative mortality reached 72% in men and 66% in women. In multivariable regression of the hazard of death on age, sex, and left ventricular ejection fraction (LVEF), age was a strong determinant of mortality and male patients had modestly higher hazard of death than female patients (adjusted hazard ratio, 1.29; 95% CI 1.18-1.41). LVEF was not a strong predictor of death. CONCLUSION: A heart failure-related hospitalization is a marker of grave prognosis: only one quarter to one third of the patients survives 5 years after admission. Both the risk of hospitalization for heart failure and the risk of subsequent death are moderately higher in men than in women. LVEF, when measured in the context of heart failure-related hospitalization, is not a strong predictor of death.