OBJECTIVES Our aim was to examine the relationships between serum hematocrit (Hct) and risk of all-cause mortality among patients with severe heart failure (HF). BACKGROUND Anemia occurs with increased frequency in severe HF. However, few studies have examined the impact of anemia on mortality in this population. METHODS Using a prospective cohort design, we evaluated the relationships between baseline serum Hct and mortality among 1,130 patients with left ventricular EF < 30% and New York Heart Association functional class 11113 or IV HF treated with angiotensin-converting enzyme inhibitors, diuretics, and digitalis. Mortality was ascertained by centralized adjudication. RESULTS The mean Hct was 41.8% (range 25.4% to 58.8%). Over 15 months of mean follow-up, there were 407 deaths (29 per 100 person-years). After adjustment for potential confounders, those in the lowest quintile of Hct (range 25.4% to 37.5%) had a 52% higher risk of death (hazard ratio 1.52, 95% confidence interval 1.11 to 2.10), compared with the highest quintile (range 46.1% to 58.8%). Within the lowest quintile of Hct, each 1% decrease in Hct was associated with an 11% higher risk of death (p < 0.01), whereas within the four higher quintiles of Hct, Hct was not associated with total mortality. Evaluation of different causes of death indicated that a lower Hct was strongly associated with death from progressive HF, rather than sudden death or other deaths. CONCLUSIONS Among patients with severe HF, anemia is a significant independent risk factor for death, with a progressively higher risk with increasing severity of anemia. Further investigation of the etiologies, prevention, and treatment of anemia in severe HF is warranted. (C) 2003 by the American College of Cardiology Foundation.